U.S. patent application number 17/437188 was filed with the patent office on 2022-06-02 for luma mapping- and chroma scaling-based video or image coding.
The applicant listed for this patent is LG ELECTRONICS INC.. Invention is credited to Seunghwan KIM, Seethal PALURI, Jie ZHAO.
Application Number | 20220174295 17/437188 |
Document ID | / |
Family ID | 1000006195454 |
Filed Date | 2022-06-02 |
United States Patent
Application |
20220174295 |
Kind Code |
A1 |
PALURI; Seethal ; et
al. |
June 2, 2022 |
LUMA MAPPING- AND CHROMA SCALING-BASED VIDEO OR IMAGE CODING
Abstract
According to the disclosure of the present document, reshaper
data and/or ALF parameters can be signaled from a parameter set on
the basis of type information, and thus the amount of data to be
signaled for video/image coding can be reduced and coding
efficiency can be increased.
Inventors: |
PALURI; Seethal; (Seoul,
KR) ; KIM; Seunghwan; (Seoul, KR) ; ZHAO;
Jie; (Seoul, KR) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
LG ELECTRONICS INC. |
Seoul |
|
KR |
|
|
Family ID: |
1000006195454 |
Appl. No.: |
17/437188 |
Filed: |
March 9, 2020 |
PCT Filed: |
March 9, 2020 |
PCT NO: |
PCT/KR2020/003237 |
371 Date: |
September 8, 2021 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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62816888 |
Mar 11, 2019 |
|
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H04N 19/189 20141101;
H04N 19/186 20141101; H04N 19/105 20141101; H04N 19/70 20141101;
H04N 19/132 20141101; H04N 19/109 20141101 |
International
Class: |
H04N 19/189 20060101
H04N019/189; H04N 19/109 20060101 H04N019/109; H04N 19/70 20060101
H04N019/70; H04N 19/105 20060101 H04N019/105; H04N 19/132 20060101
H04N019/132; H04N 19/186 20060101 H04N019/186 |
Claims
1-15. (canceled)
16. An image decoding method performed by a decoding apparatus, the
method comprising: obtaining image information from bitstream;
generating reconstructed luma samples of a current block based on
the image information; and performing a reshaping process for the
reconstructed luma sample, wherein performing the reshaping process
comprises: deriving reshaping codewords for the reshaping; and
generating modified reconstructed luma samples based on the
reconstructed luma samples and the reshaping codewords, wherein the
image information includes first header information and a first
adaptation parameter set (APS), wherein the first header
information includes reshaper related APS ID information, wherein
the reshaper related APS ID information specifies an ID of the
first APS, wherein the first APS includes type information
specifying that the first APS is an APS including the reshaper
model, wherein the first APS includes the reshaper model based on
the type information, wherein the reshaping codewords are derived
based on the reshaper model.
17. The method of claim 16, wherein the image information includes
a sequence parameter set (SPS), and wherein the SPS includes a
first reshaper enabled flag specifying whether the reshaper model
is enabled.
18. The method of claim 17, wherein the image information includes
general constraint information field, and wherein the general
constraint information field includes a constraint flag related to
presence of the reshaper model.
19. The method of claim 18, wherein the first header information
includes an indication flag specifying whether the reshaper model
is present, and wherein based on a value of the constraint flag
being equal to 1, a value of the indication flag is set to 1.
20. The method of claim 17, wherein the method further comprises
performing chroma residual scaling based on the modified
reconstructed luma samples and a chroma residual scaling flag,
wherein the chroma residual scaling flag is included in the first
header information, and wherein the chroma residual scaling flag is
signaled based on a determination that a value of the first
reshaper enabled flag is 1.
21. The method of claim 17, wherein based on a value of the first
reshaper enabled flag being 1, the first header information
includes a second reshaper enabled flag specifying whether the
reshaper model is enabled in a picture.
22. The method of claim 21, wherein based on a value of the second
reshaper enabled flag being 1, the reshaper related APS ID
information is included in the first header information.
23. The method of claim 16, wherein based on a value of the type
information being 1, the first APS includes the reshaper model
including reshaper model indices.
24. The method of claim 16, wherein the method further comprises:
generating reconstructed samples based on the modified
reconstructed luma samples; and performing an adaptive loop filter
(ALF) process on the reconstructed samples, performing the ALF
process comprises: deriving filter coefficients for the ALF
process; and generating modified reconstructed samples based on the
reconstructed samples and the filter coefficients, wherein the
image information includes a second header information and a second
APS, wherein the second header information includes ALF related APS
ID information, wherein the ALF related APS ID information
represents an ID of the second APS including the ALF data, wherein
the second APS includes type information specifying that the second
APS is an APS including an ALF data field, wherein based on a value
of the type information included in the second APS being 0, the
second APS includes the ALF data field, and wherein the filter
coefficients are derived based on the ALF data field.
25. The method of claim 24, wherein the image information includes
a sequence parameter set (SPS), and wherein the SPS includes a
first ALF enabled flag specifying whether the ALF data is
enabled.
26. The method of claim 25, wherein based on a value of the first
ALF enabled flag being 1, the second header information includes a
second ALF enabled flag specifying whether the ALF data is enabled
in a picture.
27. The method of claim 26, wherein based on a value of the second
ALF enabled flag being 1, the ALF related APS ID information is
included in the second header information.
28. The method of claim 24, wherein the ID of the first APS
indicated by the reshaper related APS ID information is different
from the ID of the second APS indicated by the ALF related APS
ID.
29. An image encoding method performed by an encoding apparatus,
the method comprising: generating reconstructed luma samples of a
current block in a current picture; generating reshaping related
information for the reconstructed luma samples; and encoding image
information including information for generating the reconstructed
luma samples and the reshaping related information, wherein the
image information includes first header information and a first
adaptation parameter set (APS), wherein the first header
information includes reshaper related APS ID information, wherein
the reshaper related APS ID information specifies an ID of the
first APS, wherein the first APS includes type information
specifying that the first APS is an APS including the reshaper
model, wherein the first APS includes the reshaper model based on
the type information, wherein the reshaper model includes
information for deriving the reshaping codewords.
30. A non-transitory computer-readable digital storage medium,
storing a bitstream of image information generated by a method, the
method comprising: generating reconstructed luma samples of a
current block in a current picture; generating reshaping related
information for the reconstructed luma samples; and encoding image
information including information for generating the reconstructed
luma samples and the reshaping related information to output a
bitstream, wherein the image information includes first header
information and a first adaptation parameter set (APS), wherein the
first header information includes reshaper related APS ID
information, wherein the reshaper related APS ID information
specifies an ID of the first APS, wherein the first APS includes
type information specifying that the first APS is an APS including
the reshaper model, wherein the first APS includes the reshaper
model based on the type information, wherein the reshaper model
includes information for deriving the reshaping codewords.
Description
BACKGROUND OF THE DISCLOSURE
Field of the Disclosure
[0001] The present document relates to luma mapping- and chroma
scaling-based video or image coding.
Related Art
[0002] Recently, demand for high-resolution, high-quality
image/video such as 4K or 8K or higher ultra high definition (UHD)
image/video has increased in various fields. As image/video data
has high resolution and high quality, the amount of information or
bits to be transmitted increases relative to the existing
image/video data, and thus, transmitting image data using a medium
such as an existing wired/wireless broadband line or an existing
storage medium or storing image/video data using existing storage
medium increase transmission cost and storage cost.
[0003] In addition, interest and demand for immersive media such as
virtual reality (VR) and artificial reality (AR) content or
holograms has recently increased and broadcasting for image/video
is having characteristics different from reality images such as
game images has increased.
[0004] Accordingly, a highly efficient image/video compression
technology is required to effectively compress, transmit, store,
and reproduce information of a high-resolution, high-quality
image/video having various characteristics as described above.
[0005] In addition, there is a discussion on techniques such as
luma mapping with chroma scaling (LMCS) and adaptive loop filtering
(ALF) to improve compression efficiency and increase
subjective/objective visual quality. In order to efficiently apply
these techniques, there is a need for a method for efficiently
signaling related information.
SUMMARY
[0006] According to an embodiment of the present document, a method
and an apparatus for increasing image coding efficiency are
provided.
[0007] According to an embodiment of the present document, an
efficient filtering application method and apparatus are
provided.
[0008] According to an embodiment of the present document, an
efficient LCMS application method and apparatus are provided.
[0009] According to an embodiment of the present document, a method
and an apparatus for hierarchically signaling ALF related
information are provided.
[0010] According to an embodiment of this document, a method and an
apparatus for hierarchically signaling LMCS related information are
provided.
[0011] According to an embodiment of the present document, LMCS
data may be signaled through APS from the parameter set based on
the type information, and APS ID information specifying the ID of
the referenced APS may be signaled through header information (tile
group header, picture header or slice header).
[0012] According to an embodiment of the present document, ALF data
may be conditionally signaled through APS, and APS ID information
specifying the ID of the referenced APS may be signaled through
header information (tile group header, picture header or slice
header).
[0013] According to an embodiment of the present document, the APS
(and/or its ID) for the derivation of ALF data may be different
from the APS (and/or its ID) for the derivation of the reshaper
data (LMCS data).
[0014] According to an embodiment of the present document,
according to a contraint flag related to the presence of a reshaper
model (reshaper, reshaper data, LMCS model, LMCS data) included in
the general constraint information field, an indication flag
indicating whether the reshaper model is present in a header
(picture header, a tile group header or a slice header) may always
be set to 1, and thus the reshaper model may always be parsed in
the header.
[0015] According to an embodiment of the present document, a
video/image decoding method performed by a decoding apparatus is
provided.
[0016] According to an embodiment of the present document, a
decoding apparatus for performing video/image decoding is
provided.
[0017] According to an embodiment of the present document, a
video/image encoding method performed by an encoding apparatus is
provided.
[0018] According to an embodiment of the present document, an
encoding apparatus for performing video/image encoding is
provided.
[0019] According to one embodiment of the present document, there
is provided a computer-readable digital storage medium in which
encoded video/image information, generated according to the
video/image encoding method disclosed in at least one of the
embodiments of the present document, is stored.
[0020] According to an embodiment of the present document, there is
provided a computer-readable digital storage medium in which
encoded information or encoded video/image information, causing to
perform the video/image decoding method disclosed in at least one
of the embodiments of the present document by the decoding
apparatus, is stored.
Advantageous Effects
[0021] According to an embodiment of the present document, overall
image/video compression efficiency may be improved.
[0022] According to an embodiment of the present document,
subjective/objective visual quality may be improved through
efficient filtering.
[0023] According to an embodiment of the present document, ALF
and/or LMCS may be adaptively applied in units of pictures, slices,
and/or coding blocks.
[0024] According to an embodiment of the present document, ALF
related information can be efficiently signaled.
[0025] According to an embodiment of the present document, LMCS
related information can be efficiently signaled.
BRIEF DESCRIPTION OF THE DRAWINGS
[0026] FIG. 1 illustrates an example of a video/image coding system
to which the embodiments of the present document may be
applied.
[0027] FIG. 2 is a diagram schematically illustrating a
configuration of a video/image encoding apparatus to which the
embodiments of the present document may be applied.
[0028] FIG. 3 is a diagram schematically illustrating a
configuration of a video/image decoding apparatus to which the
embodiments of the present document may be applied.
[0029] FIG. 4 exemplarily shows a hierarchical structure for a
coded image/video.
[0030] FIG. 5 is a flowchart schematically illustrating an example
of an ALF process.
[0031] FIG. 6 shows examples of the shapes of an ALF filters.
[0032] FIG. 7 shows an example of a hierarchical structure of ALF
data.
[0033] FIG. 8 shows another example of a hierarchical structure of
ALF data.
[0034] FIG. 9 exemplarily illustrates a hierarchical structure of a
CVS according to an embodiment of the present document.
[0035] FIG. 10 illustrates an exemplary LMCS structure according to
an embodiment of the present document.
[0036] FIG. 11 illustrates an LMCS structure according to another
embodiment of the present document.
[0037] FIG. 12 shows a graph representing an exemplary forward
mapping.
[0038] FIG. 13 and FIG. 14 schematically show an example of a
video/image encoding method and related components according to
embodiment(s) of the present document.
[0039] FIG. 15 and FIG. 16 schematically show an example of an
image/video decoding method and related components according to an
embodiment of the present document.
[0040] FIG. 17 shows an example of a content streaming system to
which embodiments disclosed in the present document may be
applied.
DESCRIPTION OF EXEMPLARY EMBODIMENTS
[0041] The present document may be modified in various forms, and
specific embodiments thereof will be described and shown in the
drawings. However, the embodiments are not intended for limiting
the present document. The terms used in the following description
are used to merely describe specific embodiments, but are not
intended to limit the present document. An expression of a singular
number includes an expression of the plural number, so long as it
is clearly read differently. The terms such as "include" and "have"
are intended to indicate that features, numbers, steps, operations,
elements, components, or combinations thereof used in the following
description exist and it should be thus understood that the
possibility of existence or addition of one or more different
features, numbers, steps, operations, elements, components, or
combinations thereof is not excluded.
[0042] Meanwhile, each configuration in the drawings described in
the present document is shown independently for the convenience of
description regarding different characteristic functions, and does
not mean that each configuration is implemented as separate
hardware or separate software. For example, two or more components
among each component may be combined to form one component, or one
component may be divided into a plurality of components.
Embodiments in which each component is integrated and/or separated
are also included in the scope of the disclosure of the present
document.
[0043] Hereinafter, examples of the present embodiment will be
described in detail with reference to the accompanying drawings. In
addition, like reference numerals are used to indicate like
elements throughout the drawings, and the same descriptions on the
like elements will be omitted.
[0044] FIG. 1 illustrates an example of a video/image coding system
to which the embodiments of the present document may be
applied.
[0045] Referring to FIG. 1, a video/image coding system may include
a first device (a source device) and a second device (a reception
device). The source device may transmit encoded video/image
information or data to the reception device through a digital
storage medium or network in the form of a file or streaming.
[0046] The source device may include a video source, an encoding
apparatus, and a transmitter. The receiving device may include a
receiver, a decoding apparatus, and a renderer. The encoding
apparatus may be called a video/image encoding apparatus, and the
decoding apparatus may be called a video/image decoding apparatus.
The transmitter may be included in the encoding apparatus. The
receiver may be included in the decoding apparatus. The renderer
may include a display, and the display may be configured as a
separate device or an external component.
[0047] The video source may acquire video/image through a process
of capturing, synthesizing, or generating the video/image. The
video source may include a video/image capture device and/or a
video/image generating device. The video/image capture device may
include, for example, one or more cameras, video/image archives
including previously captured video/images, and the like. The
video/image generating device may include, for example, computers,
tablets and smartphones, and may (electronically) generate
video/images. For example, a virtual video/image may be generated
through a computer or the like. In this case, the video/image
capturing process may be replaced by a process of generating
related data.
[0048] The encoding apparatus may encode input video/image. The
encoding apparatus may perform a series of procedures such as
prediction, transform, and quantization for compaction and coding
efficiency. The encoded data (encoded video/image information) may
be output in the form of a bitstream.
[0049] The transmitter may transmit the encoded image/image
information or data output in the form of a bitstream to the
receiver of the receiving device through a digital storage medium
or a network in the form of a file or streaming. The digital
storage medium may include various storage mediums such as USB, SD,
CD, DVD, Blu-ray, HDD, SSD, and the like. The transmitter may
include an element for generating a media file through a
predetermined file format and may include an element for
transmission through a broadcast/communication network. The
receiver may receive/extract the bitstream and transmit the
received bitstream to the decoding apparatus.
[0050] The decoding apparatus may decode the video/image by
performing a series of procedures such as dequantization, inverse
transform, and prediction corresponding to the operation of the
encoding apparatus.
[0051] The renderer may render the decoded video/image. The
rendered video/image may be displayed through the display.
[0052] The present document relates to video/image coding. For
example, a method/embodiment disclosed in the present document may
be applied to a method disclosed in the versatile video coding
(VVC) standard, the essential video coding (EVC) standard, the
AOMedia Video 1 (AV1) standard, the 2nd generation of audio video
coding standard (AVS2) or the next generation video/image coding
standard (e.g., H.267, H.268, or the like).
[0053] The present document suggests various embodiments of
video/image coding, and the above embodiments may also be performed
in combination with each other unless otherwise specified.
[0054] In the present document, a video may refer to a series of
images over time. A picture generally refers to the unit
representing one image at a particular time frame, and a slice/tile
refers to the unit constituting a part of the picture in terms of
coding. A slice/tile may include one or more coding tree units
(CTUs). One picture may consist of one or more slices/tiles. One
picture may consist of one or more tile groups. One tile group may
include one or more tiles. A brick may represent a rectangular
region of CTU rows within a tile in a picture. A tile may be
partitioned into a multiple bricks, each of which may be
constructed with one or more CTU rows within the tile. A tile that
is not partitioned into multiple bricks may also be referred to as
a brick. A brick scan may represent a specific sequential ordering
of CTUs partitioning a picture, wherein the CTUs may be ordered in
a CTU raster scan within a brick, and bricks within a tile may be
ordered consecutively in a raster scan of the bricks of the tile,
and tiles in a picture may be ordered consecutively in a raster
scan of the tiles of the picture. A tile is a rectangular region of
CTUs within a particular tile column and a particular tile row in a
picture. The tile column is a rectangular region of CTUs having a
height equal to the height of the picture and a width specified by
syntax elements in the picture parameter set. The tile row is a
rectangular region of CTUs having a height specified by syntax
elements in the picture parameter set and a width equal to the
width of the picture. A tile scan is a specific sequential ordering
of CTUs partitioning a picture in which the CTUs are ordered
consecutively in CTU raster scan in a tile whereas tiles in a
picture are ordered consecutively in a raster scan of the tiles of
the picture. A slice includes an integer number of bricks of a
picture that may be exclusively contained in a single NAL unit. A
slice may consists of either a number of complete tiles or only a
consecutive sequence of complete bricks of one tile. In the present
document, a tile group and a slice may be used in place of each
other. For example, in the present document, a tile group/tile
group header may be referred to as a slice/slice header.
[0055] Meanwhile, one picture may be divided into two or more
subpictures. A subpicture may be a rectangular region of one or
more slices within a picture.
[0056] A pixel or a pel may mean a smallest unit constituting one
picture (or image). Also, `sample` may be used as a term
corresponding to a pixel. A sample may generally represent a pixel
or a value of a pixel, and may represent only a pixel/pixel value
of a luma component or only a pixel/pixel value of a chroma
component.
[0057] A unit may represent a basic unit of image processing. The
unit may include at least one of a specific region of the picture
and information related to the region. One unit may include one
luma block and two chroma (ex. cb, cr) blocks. The unit may be used
interchangeably with terms such as block or area in some cases. In
a general case, an M.times.N block may include samples (or sample
arrays) or a set (or array) of transform coefficients of M columns
and N rows. Alternatively, the sample may mean a pixel value in the
spatial domain, and when such a pixel value is transformed to the
frequency domain, it may mean a transform coefficient in the
frequency domain.
[0058] In the present document, "A or B" may mean "only A", "only
B" or "both A and B". In other words, "A or B" in the present
document may be interpreted as "A and/or B". For example, in the
present document "A, B or C (A, B or C)" means "only A", "only B",
"only C", or "any combination of A, B and C".
[0059] A slash (/) or comma (comma) used in the present document
may mean "and/or". For example, "A/B" may mean "A and/or B".
Accordingly, "A/B" may mean "only A", "only B", or "both A and B".
For example, "A, B, C" may mean "A, B, or C".
[0060] In the present document, "at least one of A and B" may mean
"only A", "only B" or "both A and B". Also, in the present
document, the expression "at least one of A or B" or "at least one
of A and/or B" may be interpreted the same as "at least one of A
and B".
[0061] Also, in the present document, "at least one of A, B and C"
means "only A", "only B", "only C", or "any combination of A, B and
C". Also, "at least one of A, B or C" or "at least one of A, B
and/or C" may mean "at least one of A, B and C".
[0062] Also, parentheses used in the present document may mean "for
example". Specifically, when "prediction (intra prediction)" is
indicated, "intra prediction" may be proposed as an example of
"prediction". In other words, "prediction" in the present document
is not limited to "intra prediction", and "intra prediction" may be
proposed as an example of "prediction". Also, even when "prediction
(i.e., intra prediction)" is indicated, "intra prediction" may be
proposed as an example of "prediction".
[0063] Technical features that are individually described in one
drawing in the present document may be implemented individually or
simultaneously.
[0064] FIG. 2 is a diagram schematically illustrating a
configuration of a video/image encoding apparatus to which the
embodiments of the present document may be applied. Hereinafter,
what is referred to as the video encoding apparatus may include an
image encoding apparatus.
[0065] Referring to FIG. 2, the encoding apparatus 200 includes an
image partitioner 210, a predictor 220, a residual processor 230,
and an entropy encoder 240, an adder 250, a filter 260, and a
memory 270. The predictor 220 may include an inter predictor 221
and an intra predictor 222. The residual processor 230 may include
a transformer 232, a quantizer 233, a dequantizer 234, and an
inverse transformer 235. The residual processor 230 may further
include a subtractor 231. The adder 250 may be called a
reconstructor or a reconstructed block generator. The image
partitioner 210, the predictor 220, the residual processor 230, the
entropy encoder 240, the adder 250, and the filter 260 may be
configured by at least one hardware component (ex. An encoder
chipset or processor) according to an embodiment. In addition, the
memory 270 may include a decoded picture buffer (DPB) or may be
configured by a digital storage medium. The hardware component may
further include the memory 270 as an internal/external
component.
[0066] The image partitioner 210 may partition an input image (or a
picture or a frame) input to the encoding apparatus 200 into one or
more processors. For example, the processor may be called a coding
unit (CU). In this case, the coding unit may be recursively
partitioned according to a quad-tree binary-tree ternary-tree
(QTBTTT) structure from a coding tree unit (CTU) or a largest
coding unit (LCU). For example, one coding unit may be partitioned
into a plurality of coding units of a deeper depth based on a quad
tree structure, a binary tree structure, and/or a ternary
structure. In this case, for example, the quad tree structure may
be applied first and the binary tree structure and/or ternary
structure may be applied later. Alternatively, the binary tree
structure may be applied first. The coding procedure according to
the present disclosure may be performed based on the final coding
unit that is no longer partitioned. In this case, the largest
coding unit may be used as the final coding unit based on coding
efficiency according to image characteristics, or if necessary, the
coding unit may be recursively partitioned into coding units of
deeper depth and a coding unit having an optimal size may be used
as the final coding unit. Here, the coding procedure may include a
procedure of prediction, transform, and reconstruction, which will
be described later. As another example, the processor may further
include a prediction unit (PU) or a transform unit (TU). In this
case, the prediction unit and the transform unit may be split or
partitioned from the aforementioned final coding unit. The
prediction unit may be a unit of sample prediction, and the
transform unit may be a unit for deriving a transform coefficient
and/or a unit for deriving a residual signal from the transform
coefficient.
[0067] The unit may be used interchangeably with terms such as
block or area in some cases. In a general case, an M.times.N block
may represent a set of samples or transform coefficients composed
of M columns and N rows. A sample may generally represent a pixel
or a value of a pixel, may represent only a pixel/pixel value of a
luma component or represent only a pixel/pixel value of a chroma
component. A sample may be used as a term corresponding to one
picture (or image) for a pixel or a pel.
[0068] In the encoding apparatus 200, a prediction signal
(predicted block, prediction sample array) output from the inter
predictor 221 or the intra predictor 222 is subtracted from an
input image signal (original block, original sample array) to
generate a residual signal residual block, residual sample array),
and the generated residual signal is transmitted to the transformer
232. In this case, as shown, a unit for subtracting a prediction
signal (predicted block, prediction sample array) from the input
image signal (original block, original sample array) in the encoder
200 may be called a subtractor 231. The predictor may perform
prediction on a block to be processed (hereinafter, referred to as
a current block) and generate a predicted block including
prediction samples for the current block. The predictor may
determine whether intra prediction or inter prediction is applied
on a current block or CU basis. As described later in the
description of each prediction mode, the predictor may generate
various information related to prediction, such as prediction mode
information, and transmit the generated information to the entropy
encoder 240. The information on the prediction may be encoded in
the entropy encoder 240 and output in the form of a bitstream.
[0069] The intra predictor 222 may predict the current block by
referring to the samples in the current picture. The referred
samples may be located in the neighborhood of the current block or
may be located apart according to the prediction mode. In the intra
prediction, prediction modes may include a plurality of
non-directional modes and a plurality of directional modes. The
non-directional mode may include, for example, a DC mode and a
planar mode. The directional mode may include, for example, 33
directional prediction modes or 65 directional prediction modes
according to the degree of detail of the prediction direction.
However, this is merely an example, more or less directional
prediction modes may be used depending on a setting. The intra
predictor 222 may determine the prediction mode applied to the
current block by using a prediction mode applied to a neighboring
block.
[0070] The inter predictor 221 may derive a predicted block for the
current block based on a reference block (reference sample array)
specified by a motion vector on a reference picture. Here, in order
to reduce the amount of motion information transmitted in the inter
prediction mode, the motion information may be predicted in units
of blocks, sub-blocks, or samples based on correlation of motion
information between the neighboring block and the current block.
The motion information may include a motion vector and a reference
picture index. The motion information may further include inter
prediction direction (L0 prediction, L1 prediction, Bi prediction,
etc.) information. In the case of inter prediction, the neighboring
block may include a spatial neighboring block present in the
current picture and a temporal neighboring block present in the
reference picture. The reference picture including the reference
block and the reference picture including the temporal neighboring
block may be the same or different. The temporal neighboring block
may be called a collocated reference block, a co-located CU
(colCU), and the like, and the reference picture including the
temporal neighboring block may be called a collocated picture
(colPic). For example, the inter predictor 221 may configure a
motion information candidate list based on neighboring blocks and
generate information indicating which candidate is used to derive a
motion vector and/or a reference picture index of the current
block. Inter prediction may be performed based on various
prediction modes. For example, in the case of a skip mode and a
merge mode, the inter predictor 221 may use motion information of
the neighboring block as motion information of the current block.
In the skip mode, unlike the merge mode, the residual signal may
not be transmitted. In the case of the motion vector prediction
(MVP) mode, the motion vector of the neighboring block may be used
as a motion vector predictor and the motion vector of the current
block may be indicated by signaling a motion vector difference.
[0071] The predictor 220 may generate a prediction signal based on
various prediction methods described below. For example, the
predictor may not only apply intra prediction or inter prediction
to predict one block but also simultaneously apply both intra
prediction and inter prediction. This may be called combined inter
and intra prediction (CIIP). In addition, the predictor may be
based on an intra block copy (IBC) prediction mode or a palette
mode for prediction of a block. The IBC prediction mode or palette
mode may be used for content image/video coding of a game or the
like, for example, screen content coding (SCC). The IBC basically
performs prediction in the current picture but may be performed
similarly to inter prediction in that a reference block is derived
in the current picture. That is, the IBC may use at least one of
the inter prediction techniques described in the present
disclosure. The palette mode may be considered as an example of
intra coding or intra prediction. When the palette mode is applied,
a sample value within a picture may be signaled based on
information on the palette table and the palette index.
[0072] The prediction signal generated by the predictor (including
the inter predictor 221 and/or the intra predictor 222) may be used
to generate a reconstructed signal or to generate a residual
signal. The transformer 232 may generate transform coefficients by
applying a transform technique to the residual signal. For example,
the transform technique may include at least one of a discrete
cosine transform (DCT), a discrete sine transform (DST), a
karhunen-loeve transform (KLT), a graph-based transform (GBT), or a
conditionally non-linear transform (CNT). Here, the GBT means
transform obtained from a graph when relationship information
between pixels is represented by the graph. The CNT refers to
transform generated based on a prediction signal generated using
all previously reconstructed pixels. In addition, the transform
process may be applied to square pixel blocks having the same size
or may be applied to blocks having a variable size rather than
square.
[0073] The quantizer 233 may quantize the transform coefficients
and transmit them to the entropy encoder 240 and the entropy
encoder 240 may encode the quantized signal (information on the
quantized transform coefficients) and output a bitstream. The
information on the quantized transform coefficients may be referred
to as residual information. The quantizer 233 may rearrange block
type quantized transform coefficients into a one-dimensional vector
form based on a coefficient scanning order and generate information
on the quantized transform coefficients based on the quantized
transform coefficients in the one-dimensional vector form.
Information on transform coefficients may be generated. The entropy
encoder 240 may perform various encoding methods such as, for
example, exponential Golomb, context-adaptive variable length
coding (CAVLC), context-adaptive binary arithmetic coding (CABAC),
and the like. The entropy encoder 240 may encode information
necessary for video/image reconstruction other than quantized
transform coefficients (ex. values of syntax elements, etc.)
together or separately. Encoded information (ex. encoded
video/image information) may be transmitted or stored in units of
NALs (network abstraction layer) in the form of a bitstream. The
video/image information may further include information on various
parameter sets such as an adaptation parameter set (APS), a picture
parameter set (PPS), a sequence parameter set (SPS), or a video
parameter set (VPS). In addition, the video/image information may
further include general constraint information. In the present
disclosure, information and/or syntax elements transmitted/signaled
from the encoding apparatus to the decoding apparatus may be
included in video/picture information. The video/image information
may be encoded through the above-described encoding procedure and
included in the bitstream. The bitstream may be transmitted over a
network or may be stored in a digital storage medium. The network
may include a broadcasting network and/or a communication network,
and the digital storage medium may include various storage media
such as USB, SD, CD, DVD, Blu-ray, HDD, SSD, and the like. A
transmitter (not shown) transmitting a signal output from the
entropy encoder 240 and/or a storage unit (not shown) storing the
signal may be included as internal/external element of the encoding
apparatus 200, and alternatively, the transmitter may be included
in the entropy encoder 240.
[0074] The quantized transform coefficients output from the
quantizer 233 may be used to generate a prediction signal. For
example, the residual signal (residual block or residual samples)
may be reconstructed by applying dequantization and inverse
transform to the quantized transform coefficients through the
dequantizer 234 and the inverse transformer 235. The adder 250 adds
the reconstructed residual signal to the prediction signal output
from the inter predictor 221 or the intra predictor 222 to generate
a reconstructed signal (reconstructed picture, reconstructed block,
reconstructed sample array). If there is no residual for the block
to be processed, such as a case where the skip mode is applied, the
predicted block may be used as the reconstructed block. The adder
250 may be called a reconstructor or a reconstructed block
generator. The generated reconstructed signal may be used for intra
prediction of a next block to be processed in the current picture
and may be used for inter prediction of a next picture through
filtering as described below.
[0075] Meanwhile, luma mapping with chroma scaling (LMCS) may be
applied during picture encoding and/or reconstruction.
[0076] The filter 260 may improve subjective/objective image
quality by applying filtering to the reconstructed signal. For
example, the filter 260 may generate a modified reconstructed
picture by applying various filtering methods to the reconstructed
picture and store the modified reconstructed picture in the memory
270, specifically, a DPB of the memory 270. The various filtering
methods may include, for example, deblocking filtering, a sample
adaptive offset, an adaptive loop filter, a bilateral filter, and
the like. The filter 260 may generate various information related
to the filtering and transmit the generated information to the
entropy encoder 240 as described later in the description of each
filtering method. The information related to the filtering may be
encoded by the entropy encoder 240 and output in the form of a
bitstream.
[0077] The modified reconstructed picture transmitted to the memory
270 may be used as the reference picture in the inter predictor
221. When the inter prediction is applied through the encoding
apparatus, prediction mismatch between the encoding apparatus 200
and the decoding apparatus 300 may be avoided and encoding
efficiency may be improved.
[0078] The DPB of the memory 270 DPB may store the modified
reconstructed picture for use as a reference picture in the inter
predictor 221. The memory 270 may store the motion information of
the block from which the motion information in the current picture
is derived (or encoded) and/or the motion information of the blocks
in the picture that have already been reconstructed. The stored
motion information may be transmitted to the inter predictor 221
and used as the motion information of the spatial neighboring block
or the motion information of the temporal neighboring block. The
memory 270 may store reconstructed samples of reconstructed blocks
in the current picture and may transfer the reconstructed samples
to the intra predictor 222.
[0079] FIG. 3 is a schematic diagram illustrating a configuration
of a video/image decoding apparatus to which the embodiment(s) of
the present disclosure may be applied.
[0080] Referring to FIG. 3, the decoding apparatus 300 may include
an entropy decoder 310, a residual processor 320, a predictor 330,
an adder 340, a filter 350, a memory 360. The predictor 330 may
include an inter predictor 331 and an intra predictor 332. The
residual processor 320 may include a dequantizer 321 and an inverse
transformer 321. The entropy decoder 310, the residual processor
320, the predictor 330, the adder 340, and the filter 350 may be
configured by a hardware component (ex. A decoder chipset or a
processor) according to an embodiment. In addition, the memory 360
may include a decoded picture buffer (DPB) or may be configured by
a digital storage medium. The hardware component may further
include the memory 360 as an internal/external component.
[0081] When a bitstream including video/image information is input,
the decoding apparatus 300 may reconstruct an image corresponding
to a process in which the video/image information is processed in
the encoding apparatus of FIG. 2. For example, the decoding
apparatus 300 may derive units/blocks based on block partition
related information obtained from the bitstream. The decoding
apparatus 300 may perform decoding using a processor applied in the
encoding apparatus. Thus, the processor of decoding may be a coding
unit, for example, and the coding unit may be partitioned according
to a quad tree structure, binary tree structure and/or ternary tree
structure from the coding tree unit or the largest coding unit. One
or more transform units may be derived from the coding unit. The
reconstructed image signal decoded and output through the decoding
apparatus 300 may be reproduced through a reproducing
apparatus.
[0082] The decoding apparatus 300 may receive a signal output from
the encoding apparatus of FIG. 2 in the form of a bitstream, and
the received signal may be decoded through the entropy decoder 310.
For example, the entropy decoder 310 may parse the bitstream to
derive information (ex. video/image information) necessary for
image reconstruction (or picture reconstruction). The video/image
information may further include information on various parameter
sets such as an adaptation parameter set (APS), a picture parameter
set (PPS), a sequence parameter set (SPS), or a video parameter set
(VPS). In addition, the video/image information may further include
general constraint information. The decoding apparatus may further
decode picture based on the information on the parameter set and/or
the general constraint information. Signaled/received information
and/or syntax elements described later in the present disclosure
may be decoded may decode the decoding procedure and obtained from
the bitstream. For example, the entropy decoder 310 decodes the
information in the bitstream based on a coding method such as
exponential Golomb coding, CAVLC, or CABAC, and output syntax
elements required for image reconstruction and quantized values of
transform coefficients for residual. More specifically, the CABAC
entropy decoding method may receive a bin corresponding to each
syntax element in the bitstream, determine a context model using a
decoding target syntax element information, decoding information of
a decoding target block or information of a symbol/bin decoded in a
previous stage, and perform an arithmetic decoding on the bin by
predicting a probability of occurrence of a bin according to the
determined context model, and generate a symbol corresponding to
the value of each syntax element. In this case, the CABAC entropy
decoding method may update the context model by using the
information of the decoded symbol/bin for a context model of a next
symbol/bin after determining the context model. The information
related to the prediction among the information decoded by the
entropy decoder 310 may be provided to the predictor (the inter
predictor 332 and the intra predictor 331), and the residual value
on which the entropy decoding was performed in the entropy decoder
310, that is, the quantized transform coefficients and related
parameter information, may be input to the residual processor 320.
The residual processor 320 may derive the residual signal (the
residual block, the residual samples, the residual sample array).
In addition, information on filtering among information decoded by
the entropy decoder 310 may be provided to the filter 350.
Meanwhile, a receiver (not shown) for receiving a signal output
from the encoding apparatus may be further configured as an
internal/external element of the decoding apparatus 300, or the
receiver may be a component of the entropy decoder 310. Meanwhile,
the decoding apparatus according to the present disclosure may be
referred to as a video/image/picture decoding apparatus, and the
decoding apparatus may be classified into an information decoder
(video/image/picture information decoder) and a sample decoder
(video/image/picture sample decoder). The information decoder may
include the entropy decoder 310, and the sample decoder may include
at least one of the dequantizer 321, the inverse transformer 322,
the adder 340, the filter 350, the memory 360, the inter predictor
332, and the intra predictor 331.
[0083] The dequantizer 321 may dequantize the quantized transform
coefficients and output the transform coefficients. The dequantizer
321 may rearrange the quantized transform coefficients in the form
of a two-dimensional block form. In this case, the rearrangement
may be performed based on the coefficient scanning order performed
in the encoding apparatus. The dequantizer 321 may perform
dequantization on the quantized transform coefficients by using a
quantization parameter (ex. quantization step size information) and
obtain transform coefficients.
[0084] The inverse transformer 322 inversely transforms the
transform coefficients to obtain a residual signal (residual block,
residual sample array).
[0085] The predictor may perform prediction on the current block
and generate a predicted block including prediction samples for the
current block. The predictor may determine whether intra prediction
or inter prediction is applied to the current block based on the
information on the prediction output from the entropy decoder 310
and may determine a specific intra/inter prediction mode.
[0086] The predictor 320 may generate a prediction signal based on
various prediction methods described below. For example, the
predictor may not only apply intra prediction or inter prediction
to predict one block but also simultaneously apply intra prediction
and inter prediction. This may be called combined inter and intra
prediction (CIIP). In addition, the predictor may be based on an
intra block copy (IBC) prediction mode or a palette mode for
prediction of a block. The IBC prediction mode or palette mode may
be used for content image/video coding of a game or the like, for
example, screen content coding (SCC). The IBC basically performs
prediction in the current picture but may be performed similarly to
inter prediction in that a reference block is derived in the
current picture. That is, the IBC may use at least one of the inter
prediction techniques described in the present disclosure. The
palette mode may be considered as an example of intra coding or
intra prediction. When the palette mode is applied, a sample value
within a picture may be signaled based on information on the
palette table and the palette index.
[0087] The intra predictor 331 may predict the current block by
referring to the samples in the current picture. The referred
samples may be located in the neighborhood of the current block or
may be located apart according to the prediction mode. In the intra
prediction, prediction modes may include a plurality of
non-directional modes and a plurality of directional modes. The
intra predictor 331 may determine the prediction mode applied to
the current block by using a prediction mode applied to a
neighboring block.
[0088] The inter predictor 332 may derive a predicted block for the
current block based on a reference block (reference sample array)
specified by a motion vector on a reference picture. In this case,
in order to reduce the amount of motion information transmitted in
the inter prediction mode, motion information may be predicted in
units of blocks, sub-blocks, or samples based on correlation of
motion information between the neighboring block and the current
block. The motion information may include a motion vector and a
reference picture index. The motion information may further include
inter prediction direction (L0 prediction, L1 prediction, Bi
prediction, etc.) information. In the case of inter prediction, the
neighboring block may include a spatial neighboring block present
in the current picture and a temporal neighboring block present in
the reference picture. For example, the inter predictor 332 may
configure a motion information candidate list based on neighboring
blocks and derive a motion vector of the current block and/or a
reference picture index based on the received candidate selection
information. Inter prediction may be performed based on various
prediction modes, and the information on the prediction may include
information indicating a mode of inter prediction for the current
block.
[0089] The adder 340 may generate a reconstructed signal
(reconstructed picture, reconstructed block, reconstructed sample
array) by adding the obtained residual signal to the prediction
signal (predicted block, predicted sample array) output from the
predictor (including the inter predictor 332 and/or the intra
predictor 331). If there is no residual for the block to be
processed, such as when the skip mode is applied, the predicted
block may be used as the reconstructed block.
[0090] The adder 340 may be called reconstructor or a reconstructed
block generator. The generated reconstructed signal may be used for
intra prediction of a next block to be processed in the current
picture, may be output through filtering as described below, or may
be used for inter prediction of a next picture.
[0091] Meanwhile, luma mapping with chroma scaling (LMCS) may be
applied in the picture decoding process.
[0092] The filter 350 may improve subjective/objective image
quality by applying filtering to the reconstructed signal. For
example, the filter 350 may generate a modified reconstructed
picture by applying various filtering methods to the reconstructed
picture and store the modified reconstructed picture in the memory
360, specifically, a DPB of the memory 360. The various filtering
methods may include, for example, deblocking filtering, a sample
adaptive offset, an adaptive loop filter, a bilateral filter, and
the like.
[0093] The (modified) reconstructed picture stored in the DPB of
the memory 360 may be used as a reference picture in the inter
predictor 332. The memory 360 may store the motion information of
the block from which the motion information in the current picture
is derived (or decoded) and/or the motion information of the blocks
in the picture that have already been reconstructed. The stored
motion information may be transmitted to the inter predictor 260 so
as to be utilized as the motion information of the spatial
neighboring block or the motion information of the temporal
neighboring block. The memory 360 may store reconstructed samples
of reconstructed blocks in the current picture and transfer the
reconstructed samples to the intra predictor 331.
[0094] In the present document, the embodiments described in the
filter 260, the inter predictor 221, and the intra predictor 222 of
the encoding apparatus 200 may be the same as or respectively
applied to correspond to the filter 350, the inter predictor 332,
and the intra predictor 331 of the decoding apparatus 300. The same
may also apply to the unit 332 and the intra predictor 331.
[0095] As described above, in video coding, prediction is performed
to increase compression efficiency. Through this, it is possible to
generate a predicted block including prediction samples for a
current block, which is a block to be coded. Here, the predicted
block includes prediction samples in a spatial domain (or pixel
domain). The predicted block is derived equally from the encoding
device and the decoding device, and the encoding device decodes
information (residual information) on the residual between the
original block and the predicted block, not the original sample
value of the original block itself. By signaling to the device,
image coding efficiency can be increased. The decoding apparatus
may derive a residual block including residual samples based on the
residual information, and generate a reconstructed block including
reconstructed samples by summing the residual block and the
predicted block, and generate a reconstructed picture including
reconstructed blocks.
[0096] The residual information may be generated through
transformation and quantization processes. For example, the
encoding apparatus may derive a residual block between the original
block and the predicted block, and perform a transform process on
residual samples (residual sample array) included in the residual
block to derive transform coefficients, and then, by performing a
quantization process on the transform coefficients, derive
quantized transform coefficients to signal the residual related
information to the decoding apparatus (via a bitstream). Here, the
residual information may include location information, a transform
technique, a transform kernel, and a quantization parameter, value
information of the quantized transform coefficients etc. The
decoding apparatus may perform dequantization/inverse
transformation process based on the residual information and derive
residual samples (or residual blocks). The decoding apparatus may
generate a reconstructed picture based on the predicted block and
the residual block. The encoding apparatus may also
dequantize/inverse transform the quantized transform coefficients
for reference for inter prediction of a later picture to derive a
residual block, and generate a reconstructed picture based thereon.
In the present document, at least one of
quantization/dequantization and/or transform/inverse transform may
be omitted. When the quantization/dequantization is omitted, the
quantized transform coefficient may be referred to as a transform
coefficient. When the transform/inverse transform is omitted, the
transform coefficients may be called coefficients or residual
coefficients, or may still be called transform coefficients for
uniformity of expression. In the present document, a quantized
transform coefficient and a transform coefficient may be referred
to as a transform coefficient and a scaled transform coefficient,
respectively. In this case, the residual information may include
information on transform coefficient(s), and the information on the
transform coefficient(s) may be signaled through residual coding
syntax. Transform coefficients may be derived based on the residual
information (or information on the transform coefficient(s)), and
scaled transform coefficients may be derived through inverse
transform (scaling) on the transform coefficients. Residual samples
may be derived based on an inverse transform (transform) of the
scaled transform coefficients. This may be applied/expressed in
other parts of the present document as well.
[0097] Intra prediction may refer to prediction that generates
prediction samples for the current block based on reference samples
in a picture to which the current block belongs (hereinafter,
referred to as a current picture). When intra prediction is applied
to the current block, neighboring reference samples to be used for
intra prediction of the current block may be derived. The
neighboring reference samples of the current block may include
samples adjacent to the left boundary of the current block having a
size of nW.times.nH and a total of 2.times.nH samples neighboring
the bottom-left, samples adjacent to the top boundary of the
current block and a total of 2.times.nW samples neighboring the
top-right, and one sample neighboring the top-left of the current
block. Alternatively, the neighboring reference samples of the
current block may include a plurality of upper neighboring samples
and a plurality of left neighboring samples. In addition, the
neighboring reference samples of the current block may include a
total of nH samples adjacent to the right boundary of the current
block having a size of nW.times.nH, a total of nW samples adjacent
to the bottom boundary of the current block, and one sample
neighboring (bottom-right) neighboring bottom-right of the current
block.
[0098] However, some of the neighboring reference samples of the
current block may not be decoded yet or available. In this case,
the decoder may configure the neighboring reference samples to use
for prediction by substituting the samples that are not available
with the available samples. Alternatively, neighboring reference
samples to be used for prediction may be configured through
interpolation of the available samples.
[0099] When the neighboring reference samples are derived, (i) the
prediction sample may be derived based on the average or
interpolation of neighboring reference samples of the current
block, and (ii) the prediction sample may be derived based on the
reference sample present in a specific (prediction) direction for
the prediction sample among the periphery reference samples of the
current block. The case of (i) may be called non-directional mode
or non-angular mode and the case of (ii) may be called directional
mode or angular mode.
[0100] Furthermore, the prediction sample may also be generated
through interpolation between the second neighboring sample and the
first neighboring sample located in a direction opposite to the
prediction direction of the intra prediction mode of the current
block based on the prediction sample of the current block among the
neighboring reference samples. The above case may be referred to as
linear interpolation intra prediction (LIP). In addition, chroma
prediction samples may be generated based on luma samples using a
linear model. This case may be called LM mode.
[0101] In addition, a temporary prediction sample of the current
block may be derived based on filtered neighboring reference
samples, and at least one reference sample derived according to the
intra prediction mode among the existing neighboring reference
samples, that is, unfiltered neighboring reference samples, and the
temporary prediction sample may be weighted-summed to derive the
prediction sample of the current block. The above case may be
referred to as position dependent intra prediction (PDPC).
[0102] In addition, a reference sample line having the highest
prediction accuracy among the neighboring multi-reference sample
lines of the current block may be selected to derive the prediction
sample by using the reference sample located in the prediction
direction on the corresponding line, and then the reference sample
line used herein may be indicated (signaled) to the decoding
apparatus, thereby performing intra-prediction encoding. The above
case may be referred to as multi-reference line (MRL) intra
prediction or MRL based intra prediction.
[0103] In addition, intra prediction may be performed based on the
same intra prediction mode by dividing the current block into
vertical or horizontal subpartitions, and neighboring reference
samples may be derived and used in the subpartition unit. That is,
in this case, the intra prediction mode for the current block is
equally applied to the subpartitions, and the intra prediction
performance may be improved in some cases by deriving and using the
neighboring reference samples in the subpartition unit. Such a
prediction method may be called intra subpartitions (ISP) or ISP
based intra prediction.
[0104] The above-described intra prediction methods may be called
an intra prediction type separately from the intra prediction mode.
The intra prediction type may be called in various terms such as an
intra prediction technique or an additional intra prediction mode.
For example, the intra prediction type (or additional intra
prediction mode) may include at least one of the above-described
LIP, PDPC, MRL, and ISP. A general intra prediction method except
for the specific intra prediction type such as LIP, PDPC, MRL, or
ISP may be called a normal intra prediction type. The normal intra
prediction type may be generally applied when the specific intra
prediction type is not applied, and prediction may be performed
based on the intra prediction mode described above. Meanwhile,
post-filtering may be performed on the predicted sample derived as
needed.
[0105] Specifically, the intra prediction procedure may include an
intra prediction mode/type determination step, a neighboring
reference sample derivation step, and an intra prediction mode/type
based prediction sample derivation step. In addition, a
post-filtering step may be performed on the predicted sample
derived as needed.
[0106] When intra prediction is applied, the intra prediction mode
applied to the current block may be determined using the intra
prediction mode of the neighboring block. For example, the decoding
apparatus may select one of most probable mode (mpm) candidates of
an mpm list derived based on the intra prediction mode of the
neighboring block (ex. left and/or upper neighboring blocks) of the
current block based on the received mpm index and select one of the
other remaining intro prediction modes not included in the mpm
candidates (and planar mode) based on the remaining intra
prediction mode information. The mpm list may be configured to
include or not include a planar mode as a candidate. For example,
if the mpm list includes the planar mode as a candidate, the mpm
list may have six candidates. If the mpm list does not include the
planar mode as a candidate, the mpm list may have three candidates.
When the mpm list does not include the planar mode as a candidate,
a not planar flag (ex. intra_luma_not_planar_flag) indicating
whether an intra prediction mode of the current block is not the
planar mode may be signaled. For example, the mpm flag may be
signaled first, and the mpm index and not planar flag may be
signaled when the value of the mpm flag is 1. In addition, the mpm
index may be signaled when the value of the not planar flag is 1.
Here, the mpm list is configured not to include the planar mode as
a candidate does not is to signal the not planar flag first to
check whether it is the planar mode first because the planar mode
is always considered as mpm.
[0107] For example, whether the intra prediction mode applied to
the current block is in mpm candidates (and planar mode) or in
remaining mode may be indicated based on the mpm flag (ex.
Intra_luma_mpm_flag). A value 1 of the mpm flag may indicate that
the intra prediction mode for the current block is within mpm
candidates (and planar mode), and a value 0 of the mpm flag may
indicate that the intra prediction mode for the current block is
not in the mpm candidates (and planar mode). The value 0 of the not
planar flag (ex. Intra_luma_not_planar_flag) may indicate that the
intra prediction mode for the current block is planar mode, and the
value 1 of the not planar flag value may indicate that the intra
prediction mode for the current block is not the planar mode. The
mpm index may be signaled in the form of an mpm_idx or
intra_luma_mpm_idx syntax element, and the remaining intra
prediction mode information may be signaled in the form of a
rem_intra_luma_pred_mode or intra_luma_mpm_remainder syntax
element. For example, the remaining intra prediction mode
information may index remaining intra prediction modes not included
in the mpm candidates (and planar mode) among all intra prediction
modes in order of prediction mode number to indicate one of them.
The intra prediction mode may be an intra prediction mode for a
luma component (sample). Hereinafter, intra prediction mode
information may include at least one of the mpm flag (ex.
Intra_luma_mpm_flag), the not planar flag (ex.
Intra_luma_not_planar_flag), the mpm index (ex. mpm_idx or
intra_luma_mpm_idx), and the remaining intra prediction mode
information (rem_intra_luma_pred_mode or intra_luma_mpm_remainder).
In the present document, the MPM list may be referred to in various
terms such as MPM candidate list and candModeList. When MIP is
applied to the current block, a separate mpm flag (ex.
intra_mip_mpm_flag), an mpm index (ex. intra_mip_mpm_idx), and
remaining intra prediction mode information (ex.
intra_mip_mpm_remainder) for MIP may be signaled and the not planar
flag is not signaled.
[0108] In other words, in general, when block splitting is
performed on an image, a current block and a neighboring block to
be coded have similar image characteristics. Therefore, the current
block and the neighboring block have a high probability of having
the same or similar intra prediction mode. Thus, the encoder may
use the intra prediction mode of the neighboring block to encode
the intra prediction mode of the current block.
[0109] For example, the encoder/decoder may configure a list of
most probable modes (MPM) for the current block. The MPM list may
also be referred to as an MPM candidate list. Herein, the MPM may
refer to a mode used to improve coding efficiency in consideration
of similarity between the current block and neighboring block in
intra prediction mode coding. As described above, the MPM list may
be configured to include the planar mode or may be configured to
exclude the planar mode. For example, when the MPM list includes
the planar mode, the number of candidates in the MPM list may be 6.
And, if the MPM list does not include the planar mode, the number
of candidates in the MPM list may be 5.
[0110] The encoder/decoder may configure an MPM list including 5 or
6 MPMs.
[0111] In order to configure the MPM list, three types of modes can
be considered: default intra modes, neighbor intra modes, and the
derived intra modes.
[0112] For the neighboring intra modes, two neighboring blocks,
i.e., a left neighboring block and an upper neighboring block, may
be considered.
[0113] As described above, if the MPM list is configured not to
include the planar mode, the planar mode is excluded from the list,
and the number of MPM list candidates may be set to 5.
[0114] In addition, the non-directional mode (or non-angular mode)
among the intra prediction modes may include a DC mode based on the
average of neighboring reference samples of the current block or a
planar mode based on interpolation.
[0115] When inter prediction is applied, the predictor of the
encoding apparatus/decoding apparatus may derive a prediction
sample by performing inter prediction in units of blocks. Inter
prediction may be a prediction derived in a manner that is
dependent on data elements (ex. sample values or motion
information) of picture(s) other than the current picture. When
inter prediction is applied to the current block, a predicted block
(prediction sample array) for the current block may be derived
based on a reference block (reference sample array) specified by a
motion vector on the reference picture indicated by the reference
picture index. Here, in order to reduce the amount of motion
information transmitted in the inter prediction mode, the motion
information of the current block may be predicted in units of
blocks, subblocks, or samples based on correlation of motion
information between the neighboring block and the current block.
The motion information may include a motion vector and a reference
picture index. The motion information may further include inter
prediction type (L0 prediction, L1 prediction, Bi prediction, etc.)
information. In the case of inter prediction, the neighboring block
may include a spatial neighboring block present in the current
picture and a temporal neighboring block present in the reference
picture. The reference picture including the reference block and
the reference picture including the temporal neighboring block may
be the same or different. The temporal neighboring block may be
called a collocated reference block, a co-located CU (colCU), and
the like, and the reference picture including the temporal
neighboring block may be called a collocated picture (colPic). For
example, a motion information candidate list may be configured
based on neighboring blocks of the current block, and flag or index
information indicating which candidate is selected (used) may be
signaled to derive a motion vector and/or a reference picture index
of the current block. Inter prediction may be performed based on
various prediction modes. For example, in the case of a skip mode
and a merge mode, the motion information of the current block may
be the same as motion information of the neighboring block. In the
skip mode, unlike the merge mode, the residual signal may not be
transmitted. In the case of the motion vector prediction (MVP)
mode, the motion vector of the selected neighboring block may be
used as a motion vector predictor and the motion vector of the
current block may be signaled. In this case, the motion vector of
the current block may be derived using the sum of the motion vector
predictor and the motion vector difference.
[0116] The motion information may include L0 motion information
and/or L1 motion information according to an inter prediction type
(L0 prediction, L1 prediction, Bi prediction, etc.). The motion
vector in the L0 direction may be referred to as an L0 motion
vector or MVL0, and the motion vector in the L1 direction may be
referred to as an L1 motion vector or MVL1. Prediction based on the
L0 motion vector may be called L0 prediction, prediction based on
the L1 motion vector may be called L1 prediction, and prediction
based on both the L0 motion vector and the L1 motion vector may be
called bi-prediction. Here, the L0 motion vector may indicate a
motion vector associated with the reference picture list L0 (L0),
and the L1 motion vector may indicate a motion vector associated
with the reference picture list L1 (L1). The reference picture list
L0 may include pictures that are earlier in output order than the
current picture as reference pictures, and the reference picture
list L1 may include pictures that are later in the output order
than the current picture. The previous pictures may be called
forward (reference) pictures, and the subsequent pictures may be
called reverse (reference) pictures. The reference picture list L0
may further include pictures that are later in the output order
than the current picture as reference pictures. In this case, the
previous pictures may be indexed first in the reference picture
list L0 and the subsequent pictures may be indexed later. The
reference picture list L1 may further include previous pictures in
the output order than the current picture as reference pictures. In
this case, the subsequent pictures may be indexed first in the
reference picture list 1 and the previous pictures may be indexed
later. The output order may correspond to picture order count (POC)
order.
[0117] FIG. 4 exemplarily shows a hierarchical structure for a
coded image/video.
[0118] Referring to FIG. 4, coded image/video is divided into a
video coding layer (VCL) that handles the decoding process of the
image/video and itself, a subsystem that transmits and stores the
coded information, and NAL (network abstraction layer) in charge of
function and present between the VCL and the subsystem.
[0119] In the VCL, VCL data including compressed image data (slice
data) is generated, or a parameter set including a picture
parameter set (PSP), a sequence parameter set (SPS), and a video
parameter set (VPS) or a supplemental enhancement information (SEI)
message additionally required for an image decoding process may be
generated.
[0120] In the NAL, a NAL unit may be generated by adding header
information (NAL unit header) to a raw byte sequence payload (RBSP)
generated in a VCL. In this case, the RBSP refers to slice data,
parameter set, SEI message, etc., generated in the VCL. The NAL
unit header may include NAL unit type information specified
according to RBSP data included in the corresponding NAL unit.
[0121] As shown in the figure, the NAL unit may be classified into
a VCL NAL unit and a Non-VCL NAL unit according to the RBSP
generated in the VCL. The VCL NAL unit may mean a NAL unit that
includes information on the image (slice data) on the image, and
the Non-VCL NAL unit may mean a NAL unit that includes information
(parameter set or SEI message) required for decoding the image.
[0122] The above-described VCL NAL unit and Non-VCL NAL unit may be
transmitted through a network by attaching header information
according to the data standard of the subsystem. For example, the
NAL unit may be transformed into a data format of a predetermined
standard such as an H.266/VVC file format, a real-time transport
protocol (RTP), a transport stream (TS), etc., and transmitted
through various networks.
[0123] As described above, the NAL unit may be specified with the
NAL unit type according to the RBSP data structure included in the
corresponding NAL unit, and information on the NAL unit type may be
stored and signaled in the NAL unit header.
[0124] For example, the NAL unit may be classified into a VCL NAL
unit type and a Non-VCL NAL unit type according to whether the NAL
unit includes information (slice data) about an image. The VCL NAL
unit type may be classified according to the nature and type of
pictures included in the VCL NAL unit, and the Non-VCL NAL unit
type may be classified according to types of parameter sets.
[0125] The following is an example of the NAL unit type specified
according to the type of parameter set included in the Non-VCL NAL
unit type. [0126] APS (Adaptation Parameter Set) NAL unit: Type for
NAL unit including APS [0127] DPS (Decoding Parameter Set) NAL
unit: Type for NAL unit including DPS [0128] VPS (Video Parameter
Set) NAL unit: Type for NAL unit including VPS [0129] SPS(Sequence
Parameter Set) NAL unit: Type for NAL unit including SPS [0130] PPS
(Picture Parameter Set) NAL unit: Type for NAL unit including PPS
[0131] PH (Picture header) NAL unit: Type for NAL unit including
PH
[0132] The aforementioned NAL unit types may have syntax
information for the NAL unit type, and the syntax information may
be stored and signaled in a NAL unit header. For example, the
syntax information may be nal_unit_type, and NAL unit types may be
specified by a nal_unit_type value.
[0133] Meanwhile, as described above, one picture may include a
plurality of slices, and one slice may include a slice header and
slice data. In this case, one picture header may be further added
to a plurality of slices (a slice header and a slice data set) in
one picture. The picture header (picture header syntax) may include
information/parameters commonly applicable to the picture. In the
present document, a slice or a picture may be mixed or replaced
with a tile group. Also, in the present document, a slice header or
a picture header may be mixed or replaced with a tile group
header.
[0134] The slice header (slice header syntax) may include
information/parameters that may be commonly applied to the slice.
The APS (APS syntax) or the PPS (PPS syntax) may include
information/parameters that may be commonly applied to one or more
slices or pictures. The SPS (SPS syntax) may include
information/parameters that may be commonly applied to one or more
sequences. The VPS (VPS syntax) may include information/parameters
that may be commonly applied to multiple layers. The DPS (DPS
syntax) may include information/parameters that may be commonly
applied to the overall video. The DPS may include
information/parameters related to concatenation of a coded video
sequence (CVS). The high level syntax (HLS) in the present document
may include at least one of the APS syntax, the PPS syntax, the SPS
syntax, the VPS syntax, the DPS syntax, and the slice header
syntax.
[0135] In the present document, the image/image information encoded
from the encoding apparatus and signaled to the decoding apparatus
in the form of a bitstream includes not only partitioning related
information in a picture, intra/inter prediction information,
residual information, in-loop filtering information, etc, but also
information included in a slice header, information included in the
APS, information included in the PPS, information included in an
SPS, and/or information included in the VPS.
[0136] Meanwhile, in order to compensate for a difference between
an original image and a reconstructed image due to an error
occurring in a compression coding process such as quantization, an
in-loop filtering process may be performed on reconstructed samples
or reconstructed pictures as described above. As described above,
the in-loop filtering may be performed by the filter of the
encoding apparatus and the filter of the decoding apparatus, and a
deblocking filter, SAO, and/or adaptive loop filter (ALF) may be
applied. For example, the ALF process may be performed after the
deblocking filtering process and/or the SAO process are completed.
However, even in this case, the deblocking filtering process and/or
the SAO process may be omitted.
[0137] FIG. 5 is a flowchart schematically illustrating an example
of an ALF process. The ALF process disclosed in FIG. 5 may be
performed in an encoding apparatus and a decoding apparatus. In
this document, the coding apparatus may include the encoding
apparatus and/or the decoding apparatus.
[0138] Referring to FIG. 5, the coding apparatus derives a filter
for ALF (S500). The filter may include filter coefficients. The
coding apparatus may determine whether to apply the ALF, and when
determining to apply the ALF, may derive a filter including filter
coefficients for the ALF. Information for deriving a filter
(coefficients) for ALF or a filter (coefficients) for ALF may be
referred to as an ALF parameter. Information on whether ALF is
applied (i.e., ALF enabled flag) and ALF data for deriving the
filter may be signaled from the encoding apparatus to the decoding
apparatus. ALF data may include information for deriving a filter
for the ALF. Also, for example, for hierarchical control of ALF, an
ALF enabled flag may be signaled at the SPS, picture header, slice
header, and/or CTB level, respectively.
[0139] In order to derive the filter for the ALF, the activity
and/or directivity of the current block (or ALF target block) is
derived, and the filter may be derived based on the activity and/or
the directionality. For example, the ALF process may be applied in
units of 4.times.4 blocks (based on luma components). The current
block or the ALF target block may be, for example, a CU, or may be
a 4.times.4 block within a CU. Specifically, for example, filters
for ALF may be derived based on first filters derived from
information included in the ALF data and predefined second filters,
and the coding apparatus may select one of the filters based on the
activity and/or the directionality. The coding apparatus may use
filter coefficients included in the selected filter for the
ALF.
[0140] The coding apparatus performs filtering based on the filter
(S510). Modified reconstructed samples may be derived based on the
filtering. For example, the filter coefficients in the filter may
be arranged or allocated according to a filter shape, and the
filtering may be performed on reconstructed samples in the current
block. Here, the reconstructed samples in the current block may be
reconstructed samples after the deblocking filter process and the
SAO process are completed. For example, one filter shape may be
used, or one filter shape may be selected and used from among a
plurality of predetermined filter shapes. For example, a filter
shape applied to the luma component and a filter shape applied to
the chroma component may be different. For example, a 7.times.7
diamond filter shape may be used for the luma component, and a
5.times.5 diamond filter shape may be used for the chroma
component.
[0141] FIG. 6 shows examples of the shape of an ALF filter.
[0142] The (a) of FIG. 6 shows the shape of a 7.times.7 diamond
filter, and the (b) of FIG. 6 shows the shape of a 5.times.5
diamond filter. In FIG. 6, Cn in the filter shape represents a
filter coefficient. When n in Cn is the same, this indicates that
the same filter coefficients can be assigned. In the present
document, a position and/or unit to which filter coefficients are
assigned according to the filter shape of the ALF may be referred
to as a filter tab. In this case, one filter coefficient may be
assigned to each filter tap, and the arrangement of the filter taps
may correspond to a filter shape. A filter tab located at the
center of the filter shape may be referred to as a center filter
tab. The same filter coefficients may be assigned to two filter
taps of the same n value that exist at positions corresponding to
each other with respect to the center filter tap. For example, in
the case of a 7.times.7 diamond filter shape, 25 filter taps are
included, and since filter coefficients C0 to C11 are assigned in a
centrally symmetric form, filter coefficients may be assigned to
the 25 filter taps using only 13 filter coefficients. Also, for
example, in the case of a 5.times.5 diamond filter shape, 13 filter
taps are included, and since filter coefficients C0 to C5 are
assigned in a centrally symmetrical form, filter coefficients may
be assigned to the 13 filter taps using only 7 filter coefficients.
For example, in order to reduce the data amount of signaled
information on filter coefficients, 12 filter coefficients among 13
filter coefficients for the 7.times.7 diamond filter shape may be
signaled (explicitly), and one filter coefficient may be derived
(implicitly). Also, for example, 6 filter coefficients among 7
filter coefficients for a 5.times.5 diamond filter shape may be
signaled (explicitly) and one filter coefficient may be derived
(implicitly).
[0143] According to an embodiment of the present document, the ALF
parameter used for the ALF process may be signaled through an
adaptation parameter set (APS). The ALF parameter may be derived
from filter information for the ALF or ALF data.
[0144] The ALF is a type of in-loop filtering technique that can be
applied in video/image coding as described above. The ALF may be
performed using a Wiener-based adaptive filter. This may be to
minimize a mean square error (MSE) between original samples and
decoded samples (or reconstructed samples). A high level design for
an ALF tool may incorporate syntax elements accessible from the SPS
and/or slice header (or tile group header).
[0145] FIG. 7 shows an example of a hierarchical structure of ALF
data.
[0146] Referring to FIG. 7, a coded video sequence (CVS) may
include an SPS, one or more PPSs, and one or more coded pictures
that follow. Each coded picture may be divided into rectangular
regions. The rectangular regions may be referred to as tiles. One
or more tiles may be aggregated to form a tile group or slice. In
this case, the tile group header may be linked to the PPS, and the
PPS may be linked to the SPS. According to the existing method, the
ALF data (ALF parameter) is included in the tile group header.
Considering that one video consists of a plurality of pictures and
one picture includes a plurality of tiles, the frequent ALF data
(ALF parameter) signaling in units of tile groups reduces coding
efficiency.
[0147] According to an embodiment proposed in the present document,
the ALF parameter may be included in the APS and signaled as
follows.
[0148] FIG. 8 shows another example of a hierarchical structure of
ALF data.
[0149] Referring to FIG. 8, an APS is defined, and the APS may
carry necessary ALF data (ALF parameters). In addition, the APS may
have self-identification parameters and ALF data. The
self-identification parameter of the APS may include an APS ID.
That is, the APS may include information specifying the APS ID in
addition to the ALF data field. The tile group header or the slice
header may refer to the APS using APS index information. In other
words, the tile group header or the slice header may include APS
index information, and the ALF process for the target block may be
performed based on the ALF data (ALF parameter) included in the APS
having the APS ID indicated by the APS index information. Here, the
APS index information may be referred to as APS ID information.
[0150] In addition, the SPS may include a flag allowing the use of
the ALF. For example, when CVS begins, an SPS may be checked, and
the flag may be checked in the SPS. For example, the SPS may
include the syntax of Table 1 below. The syntax of Table 1 may be a
part of the SPS.
TABLE-US-00001 TABLE 1 Descriptor seq_parameter_set_rbsp( ) { ...
sps_alf_enabled_flag u(1) }
[0151] The semantics of syntax elements included in the syntax of
Table 1 may be expressed, for example, as shown in the following
table.
TABLE-US-00002 TABLE 2 sps_alf_enabled_flag equal to 0 specifies
that the adaptive loop filter is disabled. sps_alf_enabled_flag
equal to 1 specifies that the adaptive loop filter is enabled.
[0152] That is, the syntax element sps_alf_enabled_flag may
indicate whether ALF is enabled based on whether the value is 0 or
1. The syntax element sps_alf_enabled_flag may be referred to as an
ALF enabled flag (which may be referred to as a first ALF enabled
flag) and may be included in the SPS. That is, the ALF enabled flag
may be signaled in SPS (or SPS level). When the value of the ALF
enabled flag signaled by the SPS is 1, it may be determined that
the ALF is basically enabled for pictures in the CVS referring to
the SPS. Meanwhile, as described above, the ALF may be individually
turned on/off by signaling an additional enabled flag at a lower
level than the SPS.
[0153] For example, if the ALF tool is enabled for CVS, an
additional enabled flag (which may be called a second ALF enabled
flag) may be signaled in a tile group header or a slice header. The
second ALF enabled flag may be parsed/signaled, for example, when
ALF is enabled at the SPS level. If the value of the second ALF
enabled flag is 1, ALF data may be parsed through the tile group
header or the slice header. For example, the second ALF enabled
flag may specify an ALF enabling condition for luma and chroma
components. The ALF data can be accessed through APS ID
information.
TABLE-US-00003 TABLE 3 Descriptor tile_group_header ( ) {
tile_group_pic_parameter_set_id ue(v) if( sps_alf_enabled_flag ) {
tile_group_alf_enabled_flag u(1) if( tile_group_alf_enabled_flag )
tile_group_aps_id u(5) }
TABLE-US-00004 TABLE 4 Descriptor slice_header ( ) {
slice_pic_parameter_set_id ue(v) if( sps_alf_enabled_flag ) {
slice_alf_enabled_flag u(1) if( tile_group_alf_enabled_flag )
slice_aps_id u(5) }
[0154] Semantics of syntax elements included in the syntax of Table
3 or Table 4 may be expressed, for example, as shown in the
following tables.
TABLE-US-00005 TABLE 5 tile_group_alf enabled_flag equal to 1
specifies that adaptive loop filter is enabled and may be applied
to Y, Cb, or Cr color component in a tile group.
tile_group_alf_enabled_flag equal to 0 specifies that adaptive loop
filter is disabled for all color components in a tile group.
tile_group_aps_id specifies the adaptation_parameter_set_id of the
APS that the tile group refers to. The TemporalId of the APS NAL
unit having adaptation_parameter_set_id equal to tile_group_aps_id
shall be less than or equal to the TemporalId of the coded tile
group NAL unit. When multiple APSs with the same value of
adaptation_parameter_set_id are referred to by two or more tile
groups of the same picture, the multiple APSs with the same value
of adaptation_parameter_set_id shall have the same content.
TABLE-US-00006 TABLE 6 slice_alf_enabled_flag equal to 1 specifies
that adaptive loop filter is enabled and may be applied to Y, Cb,
or Cr colour component in a slice, slice_alf_enabled_flag equal to
0 specifies that adaptive loop filter is disabled for all colour
components in a slice. When not present, the value of
slice_alf_enabled_flag is inferred to be equal to
ph_alf_enabled_flag. slice_aps_id specifies the
adaptation_parameter_set_id of the APS that the slice refers to.
The TemporalId of the APS NAL unit having
adaptation_parameter_set_id equal to tile_group_aps_id shall be
less than or equal to the TemporalId of the coded slice NAL unit.
When multiple APSs with the same value of
adaptation_parameter_set_id are referred to by two or more slices
of the same picture, the multiple APSs with the same value of
adaptation_parameter_set_id shall have the same content.
[0155] The second ALF enabled flag may include the syntax element
tilegroup_alf_enabled_flag or the syntax element
slice_alf_enabled_flag.
[0156] An APS referenced by a corresponding tile group or a
corresponding slice may be identified based on the APS ID
information (i.e., the syntax element tile_group_aps_id or the
syntax element slice_aps_id). The APS may include ALF data.
[0157] Meanwhile, the structure of the APS including the ALF data
may be described based on the following syntax and semantics, for
example. The syntax of Table 7 may be a part of the APS.
TABLE-US-00007 TABLE 7 Descriptor adaptation_parameter_set_rbsp( )
{ adaptation_parameter_set_id u(5) alf_data( ) aps_extension_flag
u(1) if( aps_extension_flag ) while( more_rbsp_data( ) )
aps_extension_data_flag u(1) rbsp_trailing_bits( ) }
TABLE-US-00008 TABLE 8 adaptation_parameter_set_id provides an
identifier for the APS for reference by other syntax elements. NOTE
- APSs can be shared across pictures and can be different in
different tile groups within a picture. aps_extension_flag equal to
0 specifies that no aps_extension_data_flag syntax elements are
present in the APS RBSP syntax structure. aps_extension_flag equal
to 1 specifies that there are aps_extension_data_flag syntax
elements present in the APS RBSP syntax structure.
aps_extension_data_flag may have any value. Its presence and value
do not affect decoder conformance to profiles specified in this
version of this Specification. Decoders conforming to this version
of this Specification shall ignore all aps_extension_data_flag
syntax elements.
[0158] As described above, the syntax element
adaptation_parameter_set_id may indicate the identifier of the
corresponding APS. That is, the APS may be identified based on the
syntax element adaptation_parameter_set_id. The syntax element
adaptation_parameter_set_id may be referred to as APS ID
information. Also, the APS may include an ALF data field. The ALF
data field may be parsed/signaled after the syntax element
adaptation_parameter_set_id.
[0159] Also, for example, an APS extension flag (i.e., syntax
element aps_extension_flag) may be parsed/signaled in the APS. The
APS extension flag may indicate whether APS extension data flag
(aps_extension_data_flag) syntax elements are present. The APS
extension flag may be used, for example, to provide extension
points for a later version of the VVC standard.
[0160] Core processing/handling of ALF information may be performed
in a slice header or a tile group header. The above described ALF
data field may include information on processing of the ALF filter.
For example, information that can be extracted from the ALF data
field includes information on the number of filters used,
information specifying whether the ALF is applied only to a luma
component, information on a color component, information on an
exponential golomb (EG) parameters and/or delta values of filter
coefficients, etc.
[0161] Meanwhile, the ALF data field may include, for example, ALF
data syntax as follows.
TABLE-US-00009 TABLE 9 Descriptor alf_data( ) { alf_chroma_idc
tu(v) alf_luma_num_filters_signalled_minus1 tb(v) if(
alf_luma_num_filters_signalled_minus1 > 0 ) { for( filtIdx = 0;
filtIdx < NumAlfFilters; filtIdx++ ) alf_luma_coeff_delta_idx[
filtIdx ] tb(v) } alf_luma_coeff_delta_flag u(1) if (
!alf_luma_coeff_delta_flag &&
alf_luma_num_filters_signalled_minus1 > 0 )
alf_luma_coeff_delta_prediction_flag u(1)
alf_luma_min_eg_order_minus1 ue(v) for( i = 0; i < 3; i++ )
alf_luma_eg_order_increase_flag[ i ] u(1) if (
alf_luma_coeff_delta_flag ) { for( sigFiltIdx = 0; sigFiltIdx <=
alf_luma_num_filters_signalled_minus1; sigFiltIdx++ )
alf_luma_coeff_flag[ sigFiltIdx ] u(1) } for( sigFiltIdx = 0;
sigFiltIdx <= alf_luma_num_filters_signalled_minus1;
sigFiltIdx++ ) { if ( alf_luma_coeff_flag[ sigFiltIdx ] ) { for ( j
= 0; j < 12; j++ ) { alf_luma_coeff_delta_abs[ sigFiltIdx ][ j ]
uek(v) if( alf_luma_coeff_delta_abs[ sigFiltIdx ][ j ] )
alf_luma_coeff_delta_sign[sigFilildx ][ j ] u(1) } } } if (
alf_chroma_idc > 0) { alf_chroma_min_eg_order_minus1 ue(v) for(
i = 0; i < 2; i++ ) alf_chroma_eg_order_increase_flag[ i ] u(1)
for( j = 0; j < 6; j++) { alf_chroma_coeff_abs[ j ] uek(v) if(
alf_chroma_coeff_abs[ j ] > 0 ) alf_chroma_coeff_sign[ j ] u(1)
} } }
[0162] Semantics of syntax elements included in the syntax of Table
9 may be expressed, for example, as shown in the following
table.
TABLE-US-00010 TABLE 10 alf_chroma_idc equal to 0 specifies that
the adaptive loop filter is not applied to Cb and Cr colour
components. alf_chroma_idc equal to 1 indicates that the adaptive
loop filter is applied to the Cb colour component alf_chroma_idc
equal to 2 indicates that the adaptive loop filter is applied to
the Cr colour component. alf_chroma_idc equal to 3 indicates that
the adaptive loop filter is applied to Cb and Cr colour components.
The maximum value maxVal of the truncated unary binarization tu(v)
is set equal to 3. The variable NumAlfFilters specifying the number
of different adaptive loop filters is set equal to 25
alf_luma_num_filters_signalled_minus1 plus 1 specifies the number
of adpative loop filter c lasses for which luma coefficients can be
signalled. The value of alf_luma_num_filters_signall ed_minus1
shall be in the range of 0 to NumAlfFilters - 1, inclusive. The
maximum value maxVal of the truncated binary binarization tb(v) is
set equal to NumAlfFilters - 1 alf_luma_coeff_delta_idx[ filtIdx ]
specifies the indices of the signalled adaptive loop filter luma
coefficient deltas for the filter class indicated by filtIdx
ranging from 0 to NumAlfFilters - 1. When alf_luma_coeff delta_idx[
filtIdx ] is not present, it is inferred to be equal to 0. The
maximum value maxVal of the truncated binary binarization tb(v) is
set equal to alf_luma_num_filters_signalled_minus1.
alf_luma_coeff_delta_flag equal to 1 indicates that
alf_luma_coeff_delta_prediction_flag is not signalled.
alf_luma_coeff_delta_flag equal to 0 indicates that
alf_luma_coeff_delta_prediction_flag may be signalled.
alf_luma_coeff_delta_prediction_flag equal to 1 specifies that the
signalled luma filter coefficient deltas are predicted from the
deltas of the previous luma coefficients. alf_luma_coeff
delta_prediction_flag equal to 0 specifies that the signalled luma
filter coefficient deltas are not predicted from the deltas of the
previous luma coefficients. When not present,
alf_luma_coeff_delta_prediction_flag is inferred to be equal to 0.
alf_luma_min_eg_order_minus1 plus 1 specifies the minimum order of
the exp-Golomb code for luma filter coefficient signalling. The
value of alf_luma_min_eg_order_minus1 shall be in the range of 0 to
6, inclusive. alf_luma_eg_order_increase_flag[ i ] equal to 1
specifies that the minimum order of the exp- Golomb code for luma
filter coefficient signalling is incremented by 1.
alf_luma_eg_order_increase_flag[ i ] equal to 0 specifies that the
minimum order of the exp- Golomb code for luma filter coefficient
signalling is not incremented by 1. The order expGoOrderY[ i ] of
the exp-Golomb code used to decode the values of
alf_luma_coeff_delta_abs[ sigFiltIdx ][ j ] is derived as follows:
expGoOrderY[ i ] = alf_luma_min_eg_order_minus1 + 1+
alf_luma_eg_order_increase flag[ i ] (7-51) alf_luma_coeff_flag[
sigFiltIdx ] equal 1 specifies that the coefficients of the luma
filter indicated by sigFiltIdx are signalled. alf_luma_coeff_flag[
sigFiltIdx ] equal to 0 specifies that all filter coefficients of
the luma filter indicated by sigFiltIdx are set equal to 0. When
not present, alf_luma_coeff_flag[ sigFiltIdx ] is set equal to 1.
alf_luma_coeff_delta_abs[ sigFiltIdx ][ j ] specifies the absolute
value of the j-th coefficient delta of the signalled luma filter
indicated by sigFiltIdx. When alf_luma_coeff_delta_abs[ sigFiltIdx
][ j ] is not present, it is inferred to be equal 0. The order k of
the exp-Golomb binarization uek(v) is derived follows:
golombOrderIdxY[ ] = { 0, 0, 1, 0, 0, 1, 2, 1, 0, 0, 1, 2 } (7-52)
k = expGoOrderY[ golombOrderIdxY[ j ] ] (7-53)
alf_luma_coeff_delta_sign[ sigFiltIdx ][ j ] specifies the sign the
j-th luma coefficient of the filter indicated by sigFiltIdx as
follows: - If alf_luma_coeff_delta_sign[ sigFiltIdx ][ j ] is equal
to 0, the coressponding luma filter - coefficient has a positive
value. - Otherwise (alf_luma_coeff_delta_sign[ sigFiltIdx ][ j ] is
equal to 1), the corresponding - luma filter coefficient has a
negative value. When alf_luma_coeff_delta_sign[ sigFiltIdx ][ j ]
is not present, it is inferrred to be equal to 0. The variable
filterCoefficients[ sigFiltIdx ][ j ] with sigFiltIdx =
0..alf_luma_num_filters_signalled_minus1, j = 0..11 is initialized
as follows: filterCoefficients[ sigFiltIdx ][ j ] =
alf_luma_coeff_delta_abs[ sigFiltIdx ][ j ] * (7-54) ( 1 - 2 *
alf_luma_coeff_delta_sign[ sigFiltIdx ][ j ] ) When
alf_luma_coeff_delta_prediction_flag is equal 1,
filterCoefficients[ sigFiltIdx ][ j ] with sigFiltIdx =
1..alf_luma_num_filters_signalled_minus1 and j = 0..11 are modified
as follows: filterCoefficients[ sigFiltIdx ][ j ] +=
filterCoefficients[ sigFiltIdx - 1 ][ j ] (7-55) The luma filter
coefficients AlfCoeff.sub.L with elements AlfCoeff.sub.L[ filtIdx
][ j ], with filtIdx = 0..NumAlfFilters - 1 and j = 0..11 are
derived as follows AlfCoeff.sub.L[ filtIdx ][ j ] =
filterCoefficient[ alf_luma_coeff_delta_idx[ filtIdx ] ][ j ]
(7-56) The last filter coefficients AlfCoeff.sub.L[ filtIdx ][ 12 ]
for filtIdx = 0..NumAlfFilters - 1 are derived as follows:
AlfCoeff.sub.L[ filtIdx ][ 12 ] = 128 - .SIGMA..sub.k (
AlfCoeff.sub.L[ filtIdx ][ k ] << 1 ), with k = 0..11 It is a
requirement of bitstream conformance that the values of
AlfCoeff.sub.L[ filtIdx ][ j ] with filtIdx = 0..NumAlfFilters - 1,
j = 0..11 shall be in the range of -2.sup.7 to 2.sup.7 - 1,
inclusive and that the values of AlfCoeff.sub.L[ filtIdx ][ 12 ]
shall be in the range of 0 to 2.sup.8 - 1, inclusive.
alf_chroma_min_eg_order_minus1 plus 1 specifies the minimum order
if the exp-Golomb code for chroma filter coefficient signalling.
The value of alf_chroma_min_eg_order_minus1 shall be in the range
of 0 tp 6, inclusive. alf_chroma_eg_order_increase_flag[ i ] equal
to 1 specifies that the minimum order of the exp-Golomb code for
chroma filter coefficient signalling is incremented by 1.
alf_chroma_eg_order_increase_flag[ i ] equal to 0 specifies that
the minimum order of the exp- Golomb code for chroma filter
coefficient signalling is not incremented by 1 The order
expGoOrderC[ i ] of the exp-Golomb code used to decode the values
of alf_chroma_coeff_abs[ j ] is derived as follows: expGoOrderC[ i
] = alf_chroma_min_eg_order_minus1 + 1+
alf_chroma_eg_order_increase_f lag[ 1 ] alf_chroma_coeff_abs[ j ]
specifies the absolute value of the j-th chroma filter coefficient.
When alf_chroma_coeff_abs[ j ] is not present, it is inferred to be
equal 0. It is a requirement of bitstream conformance that the
values of alf_chroma_coeff abs[ j ] shall be in the range of 0 to
2.sup.7 - 1, inclusive. The order k of the exp-Golomb binarization
uek(v) is derived as follows: golombOrderIdxC[ ] ={ 0, 0, 1, 0, 0,
1 } (7-59) k = expGoOrderC[ golombOrderIdxC[ j ] ] (7-60)
alf_chroma_coeff_sign[ j ] specifies the sign of the j-th chroma
filter coefficient as follows: - If alf_chroma_coeff_sign[ j ] is
equal to 0, the corresponding chroma filter coefficient has a
positive value. - Otherwise (alf_chroma_coeff_sign[ j ] is equal to
1), the corresponding chroma filter coefficient has a negative
value. When alf_chroma_coeff_sign[ j ] is not present, it is
inferred to be equal to 0. The chroma filter coefficients
AlfCoeff.sub.C with elements c.sub.C[ j ], with j = 0..5 are
derived as follows: AlfCoeff.sub.C[ j ] = alf_chroma_coeff_abs[ j ]
* ( 1 - 2 * alf_chroma_coeff sign[ j ] ) (7-61) The last filter
coefficient for j = 6 is derived as follows: AlfCoeff.sub.C[ 6 ] =
128 - .SIGMA..sub.k ( AlfCoeff.sub.C[ k ] << 1 ), with k =
0..5 (7-62) It is a requirement of bitstream conformance that the
values of AlfCoeffc[ j ] with j = 0..5 shall be in the range of
-2.sup.7 - 1 to 2.sup.7 - 1, inclusive and that the values of
AlfCoeff.sub.C[ 6 ] shall be in the range of 0 to 2.sup.8 - 1,
inclusive.
[0163] For example, parsing of ALF data through a tile group header
or a slice header may start by first parsing/signaling an
alf_chroma_idc syntax element. The alf_chroma_idc syntax element
may have values ranging from 0 to 3. The values may indicate
whether the ALF based filtering process is applied only to the luma
component, or to a combination of luma and chroma components. Once
availability (enabling parameters) for each component is
determined, information on the number of luma (component) filters
may be parsed. As an example, the maximum number of filters that
can be used may be set to 25. If the number of signaled luma
filters is at least one, for each filter in the range from 0 to the
maximum number of filters (i.e., 25, which may alternatively be
known as class), index information for the filter may be
parsed/signaled. This may imply that every class (i.e., from 0 to
the maximum number of filters) is associated with a filter index.
When a filter to be used for each class is labeled based on the
filter index, a flag (i.e., alf_luma_coeff_delta_flag) may be
parsed/signaled. The flag may be used to interpret whether flag
information (i.e., alf_luma_coeff_delta_prediction_flag) related to
prediction of an ALF luma filter coefficient delta value exists in
a slice header or a tile group header.
[0164] If the number of luma filters signaled by the syntax element
alf_luma_num_filters_signalled_minus1 is greater than 0 and the
value of the syntax element alf_luma_coeff_delta_flag is 0, it
means that the syntax element alf_luma_coeff_delta_prediction_flag
is present in the slice header or tile group header and its status
is evaluated. If the state of the syntax element
alf_luma_coeff_delta_prediction_flag indicates 1, this may mean
that luma filter coefficients are predicted from previous luma
(filter) coefficients. If the state of the syntax element
alf_luma_coeff_delta_prediction_flag indicates 0, this may mean
that luma filter coefficients are not predicted from deltas of
previous luma (filter) coefficients.
[0165] When delta filter coefficients (i.e.,
alf_luma_coeff_delta_abs) are coded based on the exponential Golomb
code, order k (order-k) of the exponential Golomb (EG) code may
have to be determined in order to decode the delta luma filter
coefficients (i.e., alf_luma_coeff_delta_abs). This information may
be needed to decode the filter coefficients. The order of the
exponential Golomb code may be expressed as EG(k). In order to
determine the EG(k), the syntax element
alf_luma_min_eg_order_minus1 may be parsed/signaled. The syntax
element alf_luma_min_eg_order_minus1 may be an entropy-coded syntax
element. The syntax element alf_luma_min_eg_order_minus1 may
indicate a smallest order of an EG used for decoding the delta luma
filter coefficients. For example, the value of the syntax element
alf_luma_min_eg_order_minus1 may be in the range of 0 to 6. After
the syntax element alf_luma_min_eg_order_minus1 is parsed/signaled,
the syntax element alf_luma_eg_order_increase_flag may be
parsed/signaled. If the value of the syntax element
alf_luma_eg_order_increase_flag is 1, this indicates that the order
of the EG indicated by the syntax element
alf_luma_min_eg_order_minus1 increases by 1. If the value of the
syntax element alf_luma_eg_order_increase_flag is 0, this indicates
that the order of the EG indicated by the syntax element
alf_luma_min_eg_order_minus1 does not increase. The order of the EG
may be represented by an index of the EG. The EG order (or EG
index) (related to the luma component) based on the syntax element
alf_luma_min_eg_order_minus1 and the syntax element
alf_luma_eg_order_increase_flag may be determined, for example, as
follows.
TABLE-US-00011 TABLE 11 1. The maximum golomb index is pre-defined
according to the filter type. That is for a 5x5 filter the maximum
golomb index is 2, and for a 7x7 the maximum golomb index is 3. 2.
An initial constant, Kmin is set to be alf_luma_min_eg_order_minus1
+ 1 3. For each index, i in the range of {0 to maximum golomb
index}, intermediate array, i.e., KminTab[i] is computed,
consisting of the sum of KminTab[i] = Kmin +
alf_luma_eg_order_increase_flag[i] 4. Kmin is refreshed at the end
of each iteration to be Kmin = KminTab[i]
[0166] Based on the determination process, expGoOrderY may be
derived as expGoOrderY=KminTab. Through this, an array including EG
orders can be derived, which can be used by the decoding apparatus.
The expGoOrderY may indicate the EG order (or EG index).
[0167] There may be a pre-defined Golomb order index (i.e.,
golombOrderIdxY). The predefined Golomb order may be used to
determine a final golomb order for coding the coefficients.
[0168] For example, the predefined Golomb order may be configured
as, for example, the following.
golombOrderIdxY[ ]={0,0,1,0,1,2,1,0,0,1,2}
[0169] Here, the order k=expGoOrderY[golombOrderIdxY[j]], and j may
represent the j-th signaled filter coefficient. For example, if
j=2, that is, the third filter coefficient, golomborderIdxY[2]=1,
and thus k=expGoOrderY[1].
[0170] In this case, for example, if the value of the syntax
element alf_luma_coeff_delta_flag represents true, that is, 1, the
syntax element alf_luma_coeff_flag may be signaled for every filter
that is signaled. The syntax element alf_luma_coeff_flag indicates
whether a luma filter coefficient is (explicitly) signaled.
[0171] When the EG order and the states of the aforementioned
related flags (i.e., alf_luma_coeff_delta_flag,
alf_luma_coeff_flag, etc.) are determined, difference information
and sign information of the luma filter coefficients may be
parsed/signaled (i.e., alf_luma_coeff_flag is true), if indicated).
Delta absolute value information (alf_luma_coeff_delata_abs syntax
element) for each of the 12 filter coefficients may be
parsed/signaled. In addition, if the syntax element
alf_luma_coeff_delta_abs has a value, sign information (syntax
element alf_luma_coeff_delta_sign) may be parsed/signaled. The
information including the difference information and the sign
information of the luma filter coefficients may be referred to as
information about the luma filter coefficients.
[0172] The deltas of the filter coefficients may be determined
along with the sign and stored. In this case, the deltas of the
signed filter coefficients may be stored in the form of an array,
which may be expressed as filterCoefficients. The deltas of the
filter coefficients may be referred to as delta luma coefficients,
and the deltas of the signed filter coefficients may be referred to
as signed delta luma coefficients.
[0173] To determine the final filter coefficients from the signed
delta luma coefficients, the (luma) filter coefficients may be
updated as follows.
filterCoefficients[sigFiltIdx][j]+=filterCoefficients[sigFiltIdx][j]
[0174] Here, j may indicate a filter coefficient index, and
sigFiltIdx may indicate a signaled filter index. j={0, . . . , 11}
and sigFiltIdx={0, . . . , alf_luma_filters_signaled_minus1}.
[0175] The coefficients may be copied into the final
AlfCoeffL[filtIdx][j]. In this case, filtidx=0, . . . , 24 and j=0,
. . . , 11.
[0176] The signed delta luma coefficients for a given filter index
may be used to determine the first 12 filter coefficients. For
example, the thirteenth filter coefficient of the 7.times.7 filter
may be determined based on the following equation. The thirteenth
filter coefficient may indicate the above-described center tap
filter coefficient.
AlfCoeff.sub.L[filtIdx][12]=128-.SIGMA..sub.kAlfCoeff.sub.L[filtIdx][k]&-
lt;<1 [Equation 1]
[0177] Here, the filter coefficient index 12 may indicate a
thirteenth filter coefficient. For reference, since the filter
coefficient index starts from 0, a value of 12 may indicate a
thirteenth filter coefficient.
[0178] For example, in order to ensure bitstream conformance, the
range of the values of the final filter coefficients
AlfCoeffL[filtIdx][k] is 0, . . . , 11 may range from -27 to 27-1,
and may range from 0 to 28-1 when k is 12. Here, k may be replaced
with j.
[0179] When processing on the luma component is performed,
processing on the chroma component may be performed based on the
syntax element alf_chroma_idc. If the value of the syntax element
alf_chroma_idc is greater than 0, the minimum EG order information
for the chroma component (i.e., the syntax element
alf_chroma_min_eg_order_minus1) may be parsed/signaled. According
to the above-described embodiment of the present document, a
5.times.5 diamond filter shape may be used for the chroma
component. In this case, the maximum golomb index may be 2. In this
case, the EG order (or EG index) for the chroma component may be
determined, for example, as follows.
TABLE-US-00012 TABLE 12 1. An initial constant, Kmin is set to be
alf_chroma_min_eg_order_minus1 + 1 2. For each index, i in the
range of {0 maximum golomb index}, an intermediate array, i.e..
KminTab[i] is computed, consisting of the sum of KminTab[i] = Kmin
+ alf chroma_eg_order_increase_flag[i] 3. Kmin is refreshed at the
end of each iteration to be Kmin = KminTab[i]
[0180] Based on the determination process, expGoOrderC may be
derived as expGoOrderC=KminTab. Through this, an array including EG
orders can be derived, which can be used by the decoding apparatus.
The expGoOrderC may indicate the EG order (or EG index) for the
chroma component.
[0181] There may be a pre-defined golomb order index
(golombOrderIdxC). The pre-defined golomb order may be used to
determine a final golomb order for coding the coefficients.
[0182] For example, the pre-defined golomb order may be configured
as, for example, the following equation.
golombOrderIdxC[ ]={0,0,1,0,0,1}
[0183] Here, the order k=expGoOrderC[golombOrderIdxC[j]], and j may
represent the j-th signaled filter coefficient. For example, if
j=2, it indicates the third filter coefficient,
golomborderIdxY[2]=1, and thus k=expGoOrderC[1].
[0184] Based on this, absolute value information and sign
information of the chroma filter coefficients may be
parsed/signaled. Information including absolute value information
and sign information of the chroma filter coefficients may be
referred to as information on the chroma filter coefficients. For
example, a 5.times.5 diamond filter shape may be applied to the
chroma component, and in this case, absolute delta information (the
syntax element alf_chroma_coeff_abs) for each of the six (chroma
component) filter coefficients may be parsed/signaled. In addition,
if the value of the syntax element alf_chroma_coeff_abs is greater
than 0, sign information (the syntax element alf_chroma_coeff_sign)
may be parsed/signaled. For example, the six chroma filter
coefficients may be derived based on information on the chroma
filter coefficients. In this case, the seventh chroma filter
coefficient may be determined based on the following equation, for
example. The seventh filter coefficient may represent the
above-described center tap filter coefficient.
AlfCoeff.sub.C[6]=128-.SIGMA..sub.kAlfCoeff.sub.C[filtIdx][k]<<1
[Equation 2]
[0185] Here, the filter coefficient index 6 may indicate a seventh
filter coefficient. For reference, since the filter coefficient
index starts from 0, a value of 6 may indicate a seventh filter
coefficient.
[0186] For example, in order to ensure bitstream conformance, the
range of the values of the final filter coefficients
AlfCoeffC[filtIdx][k] may be from -2.sup.7 to 2.sup.7-1 when k is
0, . . . , 5, and the range of the values of the final filter
coefficients AlfCoeffC[filtIdx][k] may be from -2.sup.8 to
2.sup.8-1 when k is 6. Here, k may be replaced with j.
[0187] When the (luma/chroma) filter coefficients are derived, ALF
based filtering may be performed based on the filter coefficients
or a filter including the filter coefficients. Through this,
modified reconstructed samples may be derived, as described above.
In addition, multiple filters may be derived, and filter
coefficients of one of the multiple filters may be used for the ALF
process. For example, one of the plurality of filters may be
indicated based on the signaled filter selection information. Or,
for example, one of the plurality of filters may be selected based
on the activity and/or directionality of the current block or the
ALF target block, and filter coefficients of the selected filter
may be used for the ALF process.
[0188] Meanwhile, in order to increase coding efficiency, luma
mapping with chroma scaling (LMCS) may be applied as described
above. LMCS may be referred to as a loop reshaping. In order to
increase coding efficiency, LMCS control and/or signaling of LMCS
related information may be performed hierarchically.
[0189] FIG. 9 exemplarily illustrates a hierarchical structure of a
CVS according to an embodiment of the present document. A coded
video sequence (CVS) may include a sequence parameter set (SPS), a
picture parameter set (PPS), a tile group header, tile data, and/or
CTU(s). Here, the tile group header and the tile data may be
referred to as a slice header and slice data, respectively.
[0190] The SPS may include flags natively to enable tools to be
used in CVS. In addition, the SPS may be referred to by the PPS
including information on parameters that change for each picture.
Each of the coded pictures may include one or more coded
rectangular domain tiles. The tiles may be grouped into raster
scans forming tile groups. Each tile group is encapsulated with
header information called a tile group header. Each tile consists
of a CTU comprising coded data. Here the data may include original
sample values, prediction sample values, and its luma and chroma
components (luma prediction sample values and chroma prediction
sample values).
[0191] FIG. 10 illustrates an exemplary LMCS structure according to
an embodiment of the present document. The LMCS structure 1000 of
FIG. 10 includes an in-loop mapping part 1010 of luma components
based on adaptive piecewise linear (adaptive PWL) models and a
luma-dependent chroma residual scaling part 1020 for chroma
components. The dequantization and inverse transform 1011,
reconstruction 1012, and intra prediction 1013 blocks of the
in-loop mapping part 1010 represent processes applied in the mapped
(reshaped) domain. Loop filters 1015, motion compensation or inter
prediction 1017 blocks of the in-loop mapping part 1010, and
reconstruction 1022, intra prediction 1023, motion compensation or
inter prediction 1024, loop filters 1025 block of the chroma
residual scaling part 1020 represent processes applied in the
original (non-mapped, non-reshaped) domain.
[0192] As illustrated in FIG. 10, when LMCS is enabled, at least
one of the inverse mapping (reshaping) process 1014, a forward
mapping (reshaping) process 1018, and a chroma scaling process 1021
may be applied. For example, the inverse mapping process may be
applied to a (reconstructed) luma sample (or luma samples or luma
sample array) in a reconstructed picture. The inverse mapping
process may be performed based on a piecewise function (inverse)
index of a luma sample. The piecewise function (inverse) index may
identify the piece to which the luma sample belongs. Output of the
inverse mapping process is a modified (reconstructed) luma sample
(or modified luma samples or modified luma sample array). The LMCS
may be enabled or disabled at a level of a tile group (or slice),
picture or higher.
[0193] The forward mapping process and/or the chroma scaling
process may be applied to generate the reconstructed picture. A
picture may comprise luma samples and chroma samples. A
reconstructed picture with luma samples may be referred to as a
reconstructed luma picture, and a reconstructed picture with chroma
samples may be referred to as a reconstructed chroma picture. A
combination of the reconstructed luma picture and the reconstructed
chroma picture may be referred to as a reconstructed picture. The
reconstructed luma picture may be generated based on the forward
mapping process. For example, if an inter prediction is applied to
a current block, a forward mapping is applied to a luma prediction
sample derived based on a (reconstructed) luma sample in a
reference picture. Because the (reconstructed) luma sample in the
reference picture is generated based on the inverse mapping
process, the forward mapping may be applied to the luma prediction
sample thus a mapped (reshaped) luma prediction sample can be
derived. The forward mapping process may be performed based on a
piecewise function index of the luma prediction sample. The
piecewise function index may be derived based on the value of the
luma prediction sample or the value of the luma sample in the
reference picture used for inter prediction. If an intra prediction
(or an intra block copy (IBC)) is applied to the current block, the
forward mapping is not necessary because the inverse mapping
process has not applied to the reconstructed samples in the current
picture yet. A (reconstructed) luma sample in the reconstructed
luma picture is generated based on the mapped luma prediction
sample and a corresponding luma residual sample.
[0194] The reconstructed chroma picture may be generated based on
the chroma scaling process. For example, a (reconstructed) chroma
sample in the reconstructed chroma picture may be derived based on
a chroma prediction sample and a chroma residual sample (c.sub.res)
in a current block. The chroma residual sample (c.sub.res) is
derived based on a (scaled) chroma residual sample (c.sub.resScale)
and a chroma residual scaling factor (cScaleInv may be referred to
as varScale) for the current block. The chroma residual scaling
factor may be calculated based on reshaped luma prediction sample
values for the current block. For example, the scaling factor may
be calculated based on an average luma value ave(Y'.sub.pred) of
the reshaped luma prediction sample values Y'.sub.pred. For a
reference, in FIG. 10, the (scaled) chroma residual sample derived
based on the inverse transform/dequantization may be referred to as
c.sub.resScale, and the chroma residual sample derived by
performing the (inverse) scaling process to the (scaled) chroma
residual sample may be referred to as c.sub.res.
[0195] FIG. 11 illustrates an LMCS structure according to another
embodiment of the present document. FIG. 11 is described with
reference to FIG. 10. Here, the difference between the LMCS
structure of FIG. 11 and the LMCS structure 1000 of FIG. 10 is
mainly described. The in-loop mapping part and the luma-dependent
chroma residual scaling part of FIG. 11 may operate the same as
(similarly to) the in-loop mapping part 1010 and the luma-dependent
chroma residual scaling part 1020 of FIG. 10.
[0196] Referring to FIG. 11, a chroma residual scaling factor may
be derived based on luma reconstructed samples. In this case, an
average luma value (avgYr) may be obtained (derived) based on the
neighboring luma reconstructed samples outside the reconstructed
block, not the inner luma reconstructed samples of the
reconstructed block, and the chroma residual scaling factor is
derived based on the average luma value (avgYr). Here, the
neighboring luma reconstructed samples may be neighboring luma
reconstructed samples of the current block, or may be neighboring
luma reconstructed samples of virtual pipeline data units (VPDUs)
including the current block. For example, when intra prediction is
applied to the target block, reconstructed samples may be derived
based on prediction samples which are derived based on the intra
prediction. In the other example, when inter prediction is applied
to the target block, the forward mapping is applied to prediction
samples which are derived based on the inter prediction, and
reconstructed samples are generated (derived) based on the reshaped
(or forward mapped) luma prediction samples.
[0197] The video/image information signaled through the bitstream
may include LMCS parameters (information on LMCS). LMCS parameters
may be configured as high level syntax (HLS, including slice header
syntax) or the like. Detailed description and configuration of the
LMCS parameters will be described later. As described above, the
syntax tables described in the present document (and the following
embodiments) may be configured/encoded at the encoder end and
signaled to the decoder end through a bitstream. The decoder may
parse/decode information on the LMCS (in the form of syntax
elements) in the syntax tables. One or more embodiments to be
described below may be combined. The encoder may encode the current
picture based on the information about the LMCS and the decoder may
decode the current picture based on the information about the
LMCS.
[0198] The in-loop mapping of luma components may adjust the
dynamic range of the input signal by redistributing the codewords
across the dynamic range to improve compression efficiency. For
luma mapping, a forward mapping (reshaping) function (FwdMap) and
an inverse mapping (reshaping) function (InvMap) corresponding to
the forward mapping function (FwdMap) may be used. The FwdMap
function may be signaled using a piece-wise linear models, for
example, the piece-wise linear model may have 16 pieces or bins.
The pieces may have the equal length. In one example, the InvMap
function does not need to be signalled and is instead derived from
the FwdMap function. That is, the inverse mapping may be a function
of the forward mapping. For example, the inverse mapping function
may be mathematically built as the symmetric function of the
forward mapping as reflected by the line y=x.
[0199] An in-loop (luma) reshaping may be used to map input luma
values (samples) to altered values in the reshaped domain. The
reshaped values may be coded and then mapped back into the original
(un-mapped, un-reshaped) domain after reconstruction. To compensate
for the interaction between the luma signal and the chroma signal,
chroma residual scaling may be applied. In-loop reshaping is done
by specifying high level syntax for the reshaper model. The
reshaper model syntax may signal a piece-wise linear model (PWL
model). For example, the reshaper model syntax may signal a PWL
model with 16 bins or pieces of equal lengths. A forward lookup
table (FwdLUT) and/or an inverse lookup table (InvLUT) may be
derived based on the piece-wise linear model. For example, the PWL
model pre-computes the 1024-entry forward (FwdLUT) and inverse
(InvLUT) look up tables (LUT)s. As an example, when the forward
lookup table FwdLUT is derived, the inverse lookup table InvLUT may
be derived based on the forward lookup table FwdLUT. The forward
lookup table FwdLUT may map the input luma values Yi to the altered
values Yr, and the inverse lookup table InvLUT may map the altered
values Yr to the reconstructed values Y'i. The reconstructed values
Y'i may be derived based on the input luma values Yi.
[0200] In one example, the SPS may include the syntax of Table 13
below. The syntax of Table 13 may include sps_reshaper_enabled_flag
as a tool enabling flag. Here, sps_reshaper_enabled_flag may be
used to specify whether the reshaper is used in a coded video
sequence (CVS). That is, sps_reshaper_enabled_flag may be a flag
for enabling reshaping in the SPS. In one example, the syntax of
Table 13 may be a part of the SPS.
TABLE-US-00013 TABLE 13 Descriptor seq_parameter_set_rbsp( ) { ...
sps_reshaper_enabled_flag u(1) rbsp_trailing_bits( ) }
[0201] In one example, semantics on the syntax element
sps_reshaper_enabled_flag may be as shown in Table 14 below.
TABLE-US-00014 TABLE 14 sps_reshaper_enabled_flag equal to 1
specifies that reshaper is used in the coded video sequence (CVS).
sps_reshaper_enabled_flag equal to 0 specifies that reshaper is not
used in the CVS.
[0202] In one example, the tile group header may include the syntax
of Table 15 below. Hereinafter, the syntax or information referred
to together with a tile group may be replaced with a slice.
TABLE-US-00015 TABLE 15 Descriptor tile_group_header( ){ ... if(
sps_reshaper_enabled_flag) { tile_group_reshaper_model_present_flag
u(1) if(tile_group_reshaper_model_present_flag )
tile_group_reshaper_model ( ) tile_group_reshaper_enable_flag u(1)
if( tile_group_reshaper_enable_flag && (!(
qtbtt_dual_tree_intra_flag && tile_group_type == I ) ) )
tile_group_reshaper_chroma_residual_scale_flag u(1) }
byte_alignment( ) }
[0203] Semantics of syntax elements included in the syntax of Table
15 may include, for example, matters disclosed in the following
tables.
TABLE-US-00016 TABLE 16 tile_group_reshaper_model_present_flag
equal to 1 specifies tile_group_reshaper_model( ) is present in
tile group header. tile_group_reshaper_model_present_flag equal to
0 specifies tile_group_reshaper_model( ) is not present in tile
group header. When tile_group_reshaper_model_present_flag is not
present, it is inferred to be equal to 0.
tile_group_reshaper_enabled_flag equal to 1 specifies that reshaper
is enabled for the current tile group.
tile_group_reshaper_enabled_flag equal to 0 specifies that reshaper
is not enabled for the current tile group. When
tile_group_reshaper_enable_flag is not present, it is inferred to
be equal to 0. tile_group_reshaper_chroma_residual_scale_flag equal
to 1 specifies that chroma residual scaling is enabled for the
current tile group. tile_group_reshaper_chroma_residual_scale_flag
equal to 0 specifies that chroma residual scaling is not enabled
for the current tile group. When
tile_group_reshaper_chroma_residual_scale_flag is not present, it
is inferred to be equal to 0.
[0204] As one example, once the flag enabling the reshaping (i.e.,
sps_reshaper_enabled_flag) is parsed in the SPS, the tile group
header may parse additional data (i.e., information included in
Table 15 above) which is used to construct lookup tables (FwdLUT
and/or InvLUT). In order to do this, the status of the SPS reshaper
flag (sps_reshaper_enabled_flag) may be first checked in the tile
group header. When sps_reshaper_enabled_flag is true (or 1), an
additional flag, i.e., tile_group_reshaper_model_present_flag may
be parsed. The purpose of the
tile_group_reshaper_model_present_flag may be to indicate the
presence of the reshaping model. For example, when
tile_group_reshaper_model_present_flag is true (or 1), it may be
indicated that the reshaper is present for the current tile group.
When tile_group_reshaper_model_present_flag is false (or 0), it may
be indicated that the reshaper is not present for the current
tile.
[0205] If the reshaper is present and the reshaper is enabled in
the current tile, the reshaper model (i.e.,
tile_group_reshaper_model( )) may be processed. Further to this, an
additional flag, tile_group_reshaper_enable_flag may also be
parsed. The tile_group_reshaper_enable_flag may indicate whether
the reshaping model is used for the current tile group. For
example, if tile_group_reshaper_enable_flag is 0 (or false), it may
be indicated that the reshaping model is not used for the current
tile group. If tile_group_reshaper_enable_flag is 1 (or true), it
may be indicated that the reshaping model is used for the current
tile group.
[0206] As one example, tile_group_reshaper_model_present_flag may
be true (or 1) and tile_group_reshaper_enable_flag may be false (or
0). This means that the reshaping model is present but not used in
the current tile group (or slice). In this case, the reshaping
model can be used in the future tile groups (or slices). As another
example, tile_group_reshaper_enable_flag may be true (or 1) and
tile_group_reshaper_model_present_flag may be false (or 0). In such
a case, the decoder uses the reshaper from the previous
initialization.
[0207] When the reshaping model (i.e., tile_group_reshaper_model(
)) and tile_group_reshaper_enable_flag are parsed, it may be
determined (evaluated) whether conditions necessary for chroma
scaling are present. The above conditions includes a condition 1
(the current tile group/slice has not been intra-coded) and/or a
condition 2 (the current tile group/slice has not been partitioned
into two separate coding quad tree structures for luma and chroma,
i.e. the block structure for The current tile group/slice is not a
dual tree structure). If the condition 1 and/or the condition 2 are
true and/or tile_group_reshaper_enable_flag is true (or 1), then
tile_group_reshaper_chroma_residual_scale_flag may be parsed. When
tile_group_reshaper_chroma_residual_scale_flag is enabled (if 1 or
true), it may be indicated that chroma residual scaling is enabled
for the current tile group. When
tile_group_reshaper_chroma_residual_scale_flag is disabled (if 0 or
false), it may be indicated that chroma residual scaling is
disabled for the current tile group.
[0208] The purpose of the tile group reshaping model is to parse
the data that would be necessary to construct the lookup tables
(LUTs). These LUTs are constructed on the idea that the
distribution of an allowable range of luma values can be divided
into a plurality of bins (ex. 16 bins) which can be represented
using a set of 16 PWL system of equations. Therefore, any luma
value that lies within a given bin can be mapped to an altered luma
value.
[0209] FIG. 12 shows a graph representing an exemplary forward
mapping. In FIG. 12, five bins are illustrated exemplarily.
[0210] Referring to FIG. 12, the x-axis represents input luma
values, and the y-axis represents altered output luma values. The
x-axis is divided into 5 bins or slices, each bin of length L. That
is, the five bins mapped to the altered luma values have the same
length. The forward lookup table (FwdLUT) may be constructed using
data (i.e., reshaper data) available from the tile group header,
and thus mapping may be facilitated.
[0211] In one embodiment, output pivot points associated with the
bin indices may be calculated. The output pivot points may set
(mark) the minimum and maximum boundaries of the output range of
the reshaping codeword. The calculation process of the output pivot
points may be performed by computing a piecewise cumulative
distribution function (CDF) of the number of reshaping codewords.
The output pivot range may be sliced based on the maximum number of
bins to be used and the size of the lookup table (FwdLUT or
InvLUT). As one example, the output pivot range may be sliced based
on a product between the maximum number of bins and the size of the
lookup table (size of LUT*maximum number of bin indices). For
example, if the product between the maximum number of bins and the
size of the lookup table is 1024, the output pivot range may be
sliced into 1024 entries. This serration of the output pivot range
may be performed (applied or achieved) based on (using) a scaling
factor. In one example, the scaling factor may be derived based on
Equation 3 below.
SF=(y2-y1)*(1<<FP_PREC)+c [Equation 3]
[0212] In Equation 3, SF denotes a scaling factor, and y1 and y2
denote output pivot points corresponding to each bin. Also, FP_PREC
and c may be predetermined constants. The scaling factor determined
based on Equation 3 may be referred to as a scaling factor for
forward reshaping.
[0213] In another embodiment, with respect to inverse reshaping
(inverse mapping), for a defined range of the bins to be used
(i.e., from reshaper_model_min_bin_idx to
reshape_model_max_bin_idx), the input reshaped pivot points which
correspond to the mapped pivot points of the forward LUT and the
mapped inverse output pivot points (given by bin index under
consideration*number of initial codewords) are fetched. In another
example, the scaling factor SF may be derived based on Equation 4
below.
SF=(y2-y1)*(1<<FP_PREC)/(x2-x1) [Equation 4]
[0214] In Equation 4, SF denotes a scaling factor, x1 and x2 denote
input pivot points, and y1 and y2 denote output pivot points
corresponding to each piece (bin) (output pivot points of the
inverse mapping). Here, the input pivot points may be pivot points
mapped based on a forward lookup table (FwdLUT), and the output
pivot points may be pivot points inverse-mapped based on an inverse
lookup table (InvLUT). Also, FP_PREC may be a predetermined
constant value. FP_PREC of Equation 4 may be the same as or
different from FP_PREC of Equation 3. The scaling factor determined
based on Equation 4 may be referred to as a scaling factor for
inverse reshaping. During inverse reshaping, partitioning of input
pivot points may be performed based on the scaling factor of
Equation 4. The scaling factor SF is used to slice the range of
input pivot points. Based on the partitioned input pivot points,
bin indices in the range from 0 to the minimum bin index
(reshaper_model_min_bin_idx) and/or from the minimum bin index
(reshaper_model_min_bin_idx) to the maximum bin index
(reshape_model_max_bin_idx) are assigned the pivot values that
correspond to the minimum and maximum bin values.
[0215] Table 17 below shows the syntax of the reshaper model
according to an embodiment. The reshaper model may be referred to
as a reshaping model or an LMCS model. Here, the reshaper model has
been exemplarily described as a tile group reshaper, but the
present document is not necessarily limited by this embodiment. For
example, the reshaper model may be included in the APS, or the tile
group reshaper model may be referred to as a slice reshaper model
or LMCS data. Also, the prefix reshaper_model or Rsp may be used
interchangeably with lmcs. For example, in the following tables and
the description below, reshaper_model_min_bin_idx,
reshaper_model_delta_max_bin_idx, reshaper_model_max_bin_idx,
RspCW, RsepDeltaCW may be used interchangeably with
lmcs_min_bin_idx, lmcs_delta_cs_bin_idx, lmx,
lmcs_delta_csDcselta_idx, lmx, respectively.
TABLE-US-00017 TABLE 17 Descriptor tile_group_reshaper_model ( ) {
reshaper_model_min_bin_idx ue(v) reshaper_model_delta_max_bin_idx
ue(v) reshaper_model_bin_delta_abs_cw_prec_minus1 ue(v) for ( i =
reshaper_model_min_bin_idx; i <= reshaper_model_max_bin_idx; i++
) { reshape_model_bin_delta_abs_CW [ i ] u(v) if (
reshaper_model_bin_delta_abs_CW[ i ] ) > 0 )
reshaper_model_bin_delta_sign_CW_flag[ i ] u(1) } }
[0216] The semantics of syntax elements included in the syntax of
Table 17 may include, for example, descriptions in the following
table.
TABLE-US-00018 TABLE 18 reshape_model_min_bin_idx specifies the
minimum bin (or piece) index to be used in the reshaper
construction process. The value of reshape_model_min_bin_idx shall
be in the range of 0 to MaxBinIdx, inclusive. The value of
MaxBinIdx shall be equal to 15. reshape_model_delta_max_bin_idx
specifies the maximum allowed bin (or piece) index MaxBinIdx minus
the maximum bin index to be used in the reshaper construction
process. The value of reshape_model_max_bin_idx is set equal to
MaxBinIdx - reshape_model_delta_max_bin_idx.
reshaper_model_bin_delta_abs_cw_prec_minus1 plus 1 specifies the
number of bits used for the representation of the syntax
reshape_model_bin_delta_abs_CW[ i ].
reshape_model_bin_delta_abs_CW[ i ] specifies the absolute delta
codeword value for the ith bin.
reshaper_model_bin_delta_sign_CW_flag[ i ] specifies the sign of
reshape_model_bin_delta_abs_CW[ i ] as follows: - If
reshape_model_bin_delta_sign_CW_flag[ i ] is equal to 0, the
corresponding variable RspDeltaCW[ i ] is a positive value. -
Otherwise ( reshape_model_bin_delta_sign_CW_flag[ i ] is not equal
to 0 ), the corresponding variable RspDeltaCW[ i ] is a negative
value. When reshape_model_bin_delta_sign_CW_flag[ i ] is not
present, it is inferred to be equal to 0.
[0217] The reshaper model includes reshape_model_min_bin_idx,
reshape_model_delta_max_bin_idx,
reshaper_model_bin_delta_abs_cw_prec_minus1,
reshape_model_bin_delta_abs_CW[i], and
reshaper_model_bin_delta_sign_CW as elements. Hereinafter, each
syntax element will be described in detail.
[0218] reshape_model_min_bin_idx indicates the minimum bin (or
piece) index used in the reshaper configuring (constructing)
process. The value of reshape_model_min_bin_idx may range from 0 to
MaxBinIdx. For example, MaxBinIdx may be 15.
[0219] In an embodiment, the tile group reshaper model may
preferentially parse two indices (or parameters),
reshaper_model_min_bin_idx and reshaper_model_delta_max_bin_idx. A
maximum bin index (reshaper_model_max_bin_idx) may be derived
(determined) based on these two indices. The
reshape_model_delta_max_bin_idx may represent the value derived by
subtracting the actual maximum bin index
(reshape_model_max_bin_idx), used in the reshaper configuration
process, from the allowed maximum bin index MaxBinIdx. A value of
the maximum bin index (reshaper_model_max_bin_idx) may range from 0
to MaxBinIdx. For example, MaxBinIdx may be 15. As an example, the
value of reshape_model_max_bin_idx may be derived based on Equation
5 below.
reshape_model_max_bin_idx=MaxBinIdx-reshape_model_delta_max_bin_idx.
[Equation 5]
[0220] The maximum bin index reshaper_model_max_bin_idx may be
greater than or equal to the minimum bin index
reshaper_model_min_bin_idx. The minimum bin index may be referred
to as a minimum allowed bin index or a allowed minimum bin index,
and the maximum bin index may also be referred to as a maximum
allowed bin index or a allowed maximum bin index.
[0221] If the maximum bin index (rehape_model_max_bin_idx) is
derived, the syntax element
reshaper_model_bin_delta_abs_cw_prec_minus1 may be parsed. The
number of bits used to represent the syntax
reshape_model_bin_delta_abs_CW[i] may be determined based on
reshaper_model_bin_delta_abs_cw_prec_minus1. For example, the
number of bits used to represent reshape_model_bin_delta_abs_CW[i]
may be equal to 1 plus
reshaper_model_bin_delta_abs_cw_prec_minus1.
[0222] reshape_model_bin_delta_abs_CW[i] may indicate information
related to the absolute delta codeword value (absolute value of the
delta codeword) of the i-th bin. reshape_model_bin_delta_abs_CW[i]
and reshaper_model_bin_delta_sign_CW_flag[i] may be examples of
information on reshaping codewords. In one example, if the absolute
delta codeword value of the i-th bin is greater than 0,
reshaper_model_bin_delta_sign_CW_flag[i] may be parsed. A sign of
reshape_model_bin_delta_abs_CW[i] may be determined based on
reshaper_model_bin_delta_sign_CW_flag[i]. In one example, if
reshaper_model_bin_delta_sign_CW_flag[i] is 0 (or false), the
corresponding variable RspDeltaCW[i] may be a positive sign. In
other cases (if reshaper_model_bin_delta_sign_CW_flag[i] is not 0,
if reshaper_model_bin_delta_sign_CW_flag[i] is 1 (or true)), the
corresponding variable RspDeltaCW[i] may be a negative sign. If
reshape_model_bin_delta_sign_CW_flag[i] is not present, it may be
inferred to be equal to 0 (or false).
[0223] In an embodiment, the variable RspDeltaCW[i] may be derived
based on reshape_model_bin_delta_abs_CW[i] and
reshape_model_bin_delta_sign_CW_flag[i] described above.
RspDeltaCW[i] may be referred to as a value of a delta codeword.
For example, RspDeltaCW[i] may be derived based on Equation 6
below.
RspDeltaCW[i]=(1-2*reshape_model_bin_delta_sign_CW[i])*reshape_model_bin-
_delta_abs_CW[i] [Equation 6]
[0224] In Equation 6, reshape_model_bin_delta_sign_CW[i] may be
information related to a sign of RspDeltaCW[i]. For example,
reshape_model_bin_delta_sign_CW[i] may be the same as
reshaper_model_bin_delta_sign_CW_flag[i] described above. Here, i
may be in a range from a minimum bin index
(reshaper_model_min_bin_idx) to a maximum bin index
(reshape_model_max_bin_idx).
[0225] A variable (or array) RspCW[i] may be derived based on
RspDeltaCW[i]. RspDeltaCW[i] may be an example of information on
reshaping codewords. Here, RspCW[i] may indicate the number of
codewords allocated (distributed) to the i-th bin. That is, the
number of codewords allocated (distributed) to each bin may be
stored in an array form. In one example, if i is smaller than the
reshaper_model_min_bin_idx or larger than
reshaper_model_max_bin_idx (i<reshaper_model_min_bin_idx or
reshaper_model_max_bin_idx<i), RspCW[i] may be equal to 0.
Otherwise (if i is greater than or equal to
reshaper_model_min_bin_idx described above and less than or equal
to reshaper_model_max_bin_idx
(reshaper_model_min_bin_idx<=i<=reshaper_model_max_bin_idx),
RspCW[i] may be derived based on the above-described RspDeltaCW[i],
the luma bit depth (BitDepthY), and/or MaxBinIdx. In this case, for
example, RspCW[i] may be derived based on Equation 7 below.
RspCW[i]=OrgCW+RspDeltaCW[i] [Equation 7]
[0226] In Equation 7, OrgCW may be a predetermined value, for
example, may be determined based on Equation 8 below. OrgCW may be
an example of information on reshaping codewords.
OrgCW=(1<<BitDepth.sub.Y)/(MaxBinIdx+1) [Equation 8]
[0227] In Equation 8, BitDepthY is the luma bit depth, and
MaxBinIdx represents the allowable maximum bin index. In one
example, if BitDepthY is 10, RspCW[i] may have a value from 32 to
2*OrgCW-1.
[0228] A variable InputPivot[i] may be derived based on the OrgCW.
For example, InputPivot[i] may be derived based on Equation 9
below.
InputPivot[i]=i*OrgCW [Equation 9]
[0229] Variables ReshapePivot[i], ScaleCoef[i], and/or
InvScaleCoeff[i] may be derived based on the above-described
RspCW[i], InputPivot[i], and/or OrgCW, for example,
ReshapePivot[i]], ScaleCoef[i], and/or InvScaleCoeff[i] may be
derived based on the following table.
TABLE-US-00019 TABLE 19 shiftY = 14 ReshapePivot[ 0 ] = 0; for( i =
0; i <= MaxBinIdx ; i++) { ReshapePivot[ i + 1 ] = ReshapePivot[
i ] + RspCW[ i ] ScaleCoef[ i ] = ( RspCW[ i ] * (1 <<
shiftY) + (1 << (Log2(OrgCW) - 1))) >> (Log2(OrgCW)) if
( RspCW[ i ] == 0 ) InvScaleCoeff[ i ] = 0 else InvScaleCoeff[ i ]
= OrgCW * (1 << shiftY) / RspCW[ i ] }
[0230] In Table 19, the for loop syntax in which i increases from 0
to MaxBinIdx may be used, and shiftY may be a predetermined
constant for bit shifting. Whether InvScaleCoeff[i] is derived
based on RspCW[i] may be determined based on a conditional clause
according to whether RspCW[i] is 0.
[0231] ChromaScaleCoef[i] for deriving the chroma residual scaling
factor may be derived based on the following table. Here, i may
range from 0 to MaxBinIdx.
TABLE-US-00020 TABLE 20 ChromaResidualScaleLut[64] = {16384, 16384,
16384, 16384, 16384, 16384, 16384, 8192, 8192, 8192, 8192, 5461,
5461, 5461, 5461, 4096, 4096, 4096, 4096, 3277, 3277, 3277, 3277,
2731, 2731, 2731, 2731, 2341, 2341, 2341, 2048, 2048, 2048, 1820,
1820, 1820, 1638, 1638, 1638, 1638, 1489, 1489, 1489, 1489, 1365,
1365, 1365, 1365, 1260, 1260, 1260, 1260, 1170, 1170, 1170, 1170,
1092, 1092, 1092, 1092, 1024, 1024, 1024, 1024}; shiftC = 11 - if (
RspCW[ i ] == 0 ) ChromaScaleCoef [ i ] = (1 << shiftC) -
Otherwise (RspCW[ i ] != 0), ChromaScaleCoef[ i ] =
ChromaResidualScaleLut[RspCW[ i ] >> 1]
[0232] In Table 20, shiftC may be a predetermined constant for bit
shifting. Referring to Table 20, whether ChromaScaleCoef[i] is
derived based on the array ChromaResidualScaleLut may be determined
based on a conditional clause according to whether RspCW[i] is 0.
Here, ChromaResidualScaleLut may be a predetermined array. However,
the array ChromaResidualScaleLut is merely exemplary, and the
present embodiment is not necessarily limited by Table 20.
[0233] A method for deriving the i-th variables has been described
above. The i+1-th variables may be based on ReshapePivot[i+1], and
for example, ReshapePivot[i+1] may be derived based on Equation
10.
ReshapePivot[i+1]=ReshapePivot[i]+RspCW[i] [Equation 10]
[0234] In Equation 10, RspCW[i] may be derived based on Equations 7
and/or 8 described above. Luma mapping may be performed based on
the above-described embodiments and examples, and the
above-described syntax and elements included therein may be merely
exemplary representations, and embodiments are not limited by the
above-mentioned tables or equations.
[0235] The (luma-dependent) chroma residual scaling is designed to
compensate for the interaction between the luma signal and its
corresponding chroma signals. For example, whether chroma residual
scaling is enabled or not is also signalled at the tile group level
or the slice level. In one example, if luma mapping is enabled and
if dual tree partition (also known as separate chroma tree) is not
applied to the current tile group, an additional flag is signalled
to indicate if the luma-dependent chroma residual scaling is
enabled or not. In other example, when luma mapping is not used, or
when dual tree partition is used in the current tile group,
luma-dependent chroma residual scaling is disabled. In another
example, the luma-dependent chroma residual scaling is always
disabled for the chroma blocks whose area is less than or equal to
4.
[0236] Chroma residual scaling may be performed based on an average
luma value of reference samples. For example, the reference samples
may include samples of a corresponding luma prediction block (a
luma component of a prediction block to which intra prediction
and/or inter prediction is applied). When the inter prediction is
applied, the reference samples may include samples after forward
mapping is applied to the luma component prediction samples.
Alternatively, the reference samples may include neighboring
samples of the current block or neighboring samples of a VPDU
including the current block. In this case, when the inter
prediction is applied to the neighboring block including the
neighboring samples, the neighboring samples may include luma
component reconstruction samples derived based on the luma
component prediction samples to which the forward mapping of the
neighboring block is applied. Scaling operations at the encoder
side and/or the decoder side may be implemented as, for example,
fixed-point integer operations based on Equation 11 below.
c'=sign(c)*((abs(c)*s+2CSCALE_FP_PREC-1)>>CSCALE_FP_PREC)
[Equation 11]
[0237] In Equation 11, c' denotes a scaled chroma residual sample
(scaled chroma component of a residual sample), c denotes a chroma
residual sample (chroma component of residual sample), s denotes a
chroma residual scaling factor, and CSCALE_FP_PREC denotes a
(predefined) constant value.
[0238] As described above, the average luma value of the reference
samples may be obtained, and the chroma residual scaling factor may
be derived based on the average luma value. As described above, the
chroma component residual samples may be scaled based on the chroma
residual scaling factor, and a chroma component reconstructed
sample may be generated based on the scaled chroma component
residual samples.
[0239] In an embodiment of the present document, a signaling
structure for efficiently applying the above-described ALF and/or
LMCS is proposed. According to an embodiment of the present
document, for example, ALF data and/or LMCS data (i.e., reshaper
data) may be included in the HLS (i.e., APS), and ALF data and/or
LMCS data (reshaper data) included in the APS may be derived by
signaling the referenced APS ID. Also, for example, each APS may
include type information regarding parameter types of parameters in
a corresponding parameter set.
[0240] For example, the following table shows an example of a
sequence parameter set and semantics of syntax elements included
therein according to an embodiment.
TABLE-US-00021 TABLE 21 Descriptor seq_parameter_set_rbsp( ) { . .
. sps_reshaper_enabled_flag u(1) ... }
TABLE-US-00022 TABLE 22 sps_reshaper_enabled_flag equal to 1
specifies that reshaper is used in the coded video sequence (CVS).
sps_reshaper_enabled_flag equal to 0 specifies that reshaper is not
used in the CVS.
[0241] For example, the following table shows an example of an
adaptation parameter set (APS) according to an embodiment.
TABLE-US-00023 TABLE 23 Descriptor adaptation_parameter_set_rbsp( )
{ adaptation_parameter_set_id u(5) aps_params_type u(3) if(
aps_params_type == ALF_APS ) alf_data( ) else if ( aps_params_type
== MAP_APS ) reshaper_data( ) aps_extension_flag u(1) if(
aps_extension_flag ) while( more_rbsp_data( ) )
aps_extension_data_flag u(1) rbsp_trailing_bits( ) }
[0242] Table 23 will be described based on the difference from the
APS of Table 7 described above. As an example, type information
(i.e., aps_params_type) of APS parameters may be parsed/signaled in
the APS. Type information of APS parameters may be parsed/signaled
after adaptation_parameter_set_id.
[0243] The aps_params_type, ALF_APS, and MAP_APS included in Table
23 may be described according to the following table. That is,
according to the aps_params_type included in Table 23, the types of
APS parameters applied to the APS may be set as shown in the
following table.
TABLE-US-00024 TABLE 24 Name of aps_params_type aps_params_type
Type of APS parameters 0 ALF_APS ALF parameters 1 MAP_APS In-loop
mapping (i.e., reshaper) parameters 2 . . . 7 Reserved Reserved
[0244] Referring to Table 24, for example, aps_params_type may be a
syntax element for classifying types of corresponding APS
parameters. The type of APS parameters may include ALF parameters
and in-loop mapping (i.e., reshaper) parameters. Referring to Table
24, when the value of type information (aps_params_type) is 0, the
name of aps_params_type may be determined as ALF_APS (or ALF APS),
and the type of APS parameters may be determined as ALF parameters
(APS parameter may indicate ALF parameters in this case). In this
case, the ALF data field (i.e. alf_data( )) may be parsed/signaled
to the APS. When the value of type information (aps params_type) is
1, the name of aps_params_type may be determined as MAP_APS (or
reshaper APS), and the type of APS parameters may be determined as
in-loop mapping (i.e., reshaper) parameters (APS parameters may
indicate reshaper parameters). In this case, reshaper (reshaper
model, LMCS) data (i.e., reshaper_data( )) may be parsed/signaled
to the APS.
[0245] As an example, the following table shows an example of
header information according to an embodiment. Here, the tile group
header may be referred to as a picture header or a slice
header.
TABLE-US-00025 TABLE 25 Descriptor tile_group_header( ) { ... if(
sps_alf_enabled_flag ) { tile_group_alf_enabled_flag u(1) if(
tile_group_alf_enabled_flag ) tile_group_alf_aps_id u(5) } ... if(
sps_reshaper_enabled_flag) { tile_group_reshaper_enable_flag u(1)
if( tile_group_reshaper_enable_flag ) { tile_group_reshaper_aps_id
u(5) if( !( qtbtt_dual_tree_intra_flag && tile_group_ type
== I ) ) tile_group_reshaper_chroma_residual_scale_flag u(1) } }
... if( NumTilesInCurrTileGroup > 1 ) { offset_len_minus1 ue(v)
for( i = 0; i < NumTilesInCurrTileGroup - 1; i++ )
entry_point_offset_minus1[ i ] u(v) } byte_alignment( ) }
[0246] The semantics of syntax elements included in the syntax of
Table 25 may include, for example, matters disclosed in the
following table. Here, tile_group_reshaper_enable_flag may be
referred to as slice_reshaper_enable_flag, ph_reshaper_enable_flag,
and ph_lmcs_enable_flag. That is, tie_group_reshaper_enable_flag
and slice_reshaper_enable_flag may indicate whether reshaper data
is enabled in a tile or slice (reshaper enabled flag). The
tile_group_reshaper_enable_flag is different from
sps_reshaper_enable_flag, and specifically, each flag may be
present for different layers.
[0247] In one example, the image information may include a first
APS, a second APS, and header information. The header information
may include reshaper related APS ID information (ex.
tie_group_alf_aps_id) and ALF related APS ID information (ex.
tie_group_alf_aps_id). The reshaper related APS ID information (ex.
tile_group_alf_aps_id) may indicate the first APS and/or its ID.
The ALF related APS ID information (ex. tile_group_alf_aps_id) may
indicate the second APS and/or its ID. For example, the ID of the
first APS may be different from the ID of the second APS.
TABLE-US-00026 TABLE 26 tile_group_alf_aps_id specifies the
adaptation_parameter_set_id of the ALF APS that the tile group
refers to. The TemporalId of the ALF APS NAL unit having
adaptation_parameter_set_id equal to tile_group_alf_aps_id shall be
less than or equal to the TemporalId of the coded tile group NAL
unit. When multiple ALF APSs with the same value of
adaptation_parameter_set_id are referred to by two or more tile
groups of the same picture, the multiple ALF APSs with the same
value of adaptation_parameter_set_id shall have the same content.
tile_group_reshaper_enabled_flag equal to 1 specifies that reshaper
is enabled for the current tile group.
tile_group_reshaper_enabled_flag equal to 0 specifies that reshaper
is not enabled for the current tile group. When
tile_group_reshaper_enable_flag is not present, it is inferred to
be equal to 0. tile_group_reshaper_aps_id specifies the
adaptation_parameter_set_id of the reshaper APS that the tile group
refers to. The TemporalId of the reshaper APS NAL unit having
adaptation_parameter_set_id equal to tile_group_reshaper_aps_id
shall be less than or equal to the TemporalId of the coded tile
group NAL unit. When multiple reshaper APSs with the same value of
adaptation_parameter_set_id are referred to by two or more tile
groups of the same picture, the multiple reshaper APSs with the
same value of adaptation_parameter_set_id shall have the same
content. tile_group_reshaper_chroma_residual_scale_flag equal to 1
specifies that chroma residual scaling is enabled for the current
tile group. tile_group_reshaper_chroma_residual_scale_flag equal to
0 specifies that chroma residual scaling is not enabled for the
current tile group. When
tile_group_reshaper_chroma_residual_scale_flag is not present, it
is inferred to be equal to 0.
[0248] The following table shows exemplary syntax of reshaper data
(referred to as a reshaper model, or simply reshaper) according to
an embodiment of the present document. The reshaper data shown in
the syntax of Table 27 may be an example of the reshaper data field
included in Table 23.
TABLE-US-00027 TABLE 27 Descriptor reshaper_data( ) {
reshaper_model_min_bin_idx ue(v) reshaper_model_delta_max_bin_idx
ue(v) reshaper_model_bin_delta_abs_cw_prec_minus1 ue(v) for ( i =
reshaper_model_min_bin_idx; i <= reshaper_model_max_bin_idx;
i++) { reshaper_model_bin_delta_abs_CW[ i ] u(v) if(
reshaper_model_bin_delta_abs_CW[ i ] ) > 0 )
reshaper_model_bin_delta_sign_CW_flag[ i ] u(1) } }
[0249] The semantics of syntax elements included in the syntax of
Table 27 may include, for example, matters disclosed in the
following table.
TABLE-US-00028 TABLE 28 reshaper_model_min_bin_idx specifies the
minimum bin (or piece) index to be used in the reshaper
construction process. The value of reshaper_model_min_bin_idx shall
be in the range of 0 to MaxBinIdx, inclusive. The value of
MaxBinIdx shall be equal to 15. reshaper_model_delta_max_bin_idx
specifies the maximum allowed bin (or piece) index MaxBinIdx minus
the maximum bin index to be used in the reshaper construction
process. The value of reshaper_model_delta_max_bin_idx shall be in
the range of 0 to MaxBinIdx, inclusive. The variable
ReshaperMaxBinIdx is set equal to MaxBinIdx -
reshaper_model_delta_max_bin_idx. The value of ReshaperMaxBinIdx
shall be greater than or equal to reshaper_model_min_bin_idx.
reshaper_model_bin_delta_abs_cw_prec_minus1 plus 1 specifies the
number of bits used for the representation of the syntax element
reshaper_model_bin_delta_abs_CW[ i ]. The value of
reshaper_model_bin_delta_abs_cw_prec_minus1 shall be in the range
of 0 to BitDepth.sub.Y - 2, inclusive.
reshaper_model_bin_delta_abs_CW[ i ] specifies the absolute delta
codeword value for the i-th bin. The
reshaper_model_bin_delta_abs_CW[ i ] syntax element is represented
by reshaper_model_bin_delta_abs_cw_prec_minus1 + 1 bits.
reshaper_model_bin_delta_sign_CW_flag[ i ] specifies the sign of
reshaper_model_bin_delta_abs_CW[ i ] as follows: If
reshape_model_bin_delta_sign_CW_flag[ i ] is equal to 0, the
corresponding variable RspDeltaCW[ i ] is a positive value. -
Otherwise ( reshape_model_bin_delta_sign_CW_flag[ i ] is not equal
to 0 ), the corresponding variable RspDeltaCW[ i ] is a negative
value. When reshape_model_bin_delta_sign_CW_flag[ i ] is not
present, it is inferred to be equal to 0.
[0250] In an embodiment of the present document, a method of
resetting (or constraining reshaping/mapping/LMCS) the in-loop
reshaper using a constraint flag is proposed. Specifically,
reshaper_model_present_constraint_flag may be defined as an
exemplary syntax element. This example syntax element can be used
to specify conformance bitstream properties. In the tables below,
the syntax and semantics of the constraint flag will be
described.
[0251] In one example, image information (or encoded image
information) obtained through a bitstream may include syntax (i.e.,
general constraint information syntax) as shown in the following
table.
TABLE-US-00029 TABLE 29 Descriptor general_constraint_info( ) { . .
. reshaper_model_present_constraint_flag u(1) . . . }
[0252] For example, general_constraint_info( ) may be referred to
as a general constraint information field or information on
constraint flags.
[0253] The semantics of syntax elements included in the syntax of
Table 29 may include, for example, matters disclosed in the
following table.
TABLE-US-00030 TABLE 30 reshaper_model_present_constraint_flag
equal to 1 specifies that it is a requirement of bitstream
conformance that tile_group_reshaper_model_present_flag shall be
equal to 1. reshaper_model_present_constraint_flag equal to 0 does
not impose a constraint.
[0254] The tile_group_reshaper_model_present_flag included in Table
30 may be substantially the same as the
tile_group_reshaper_model_present_flag included in Table 15
described above. According to the above-described embodiment
including a constraint flag (ex.
reshaper_model_present_constraint_flag), the reshaping model
(reshaping model, reshaper, LMCS model, LMCS data) can always be
parsed (i.e., for intra random access point (IRAP) picture, or for
intra mode).
[0255] The constraint flag may include, for example, a constraint
flag for reshaping (or mapping, LMCS). The constraint flag for
reshaping (or mapping, LMCS) may specify that reshaping (or
mapping, LMCS) is constrained (i.e., not available) for the entire
video (pictures in a plurality of sequences).
[0256] In one example, image information (or encoded image
information) obtained through a bitstream may include syntax (i.e.,
general restriction information syntax) as shown in the following
table.
TABLE-US-00031 TABLE 31 Descriptor general_constraint_info( ){ ...
no_lmcs_constraint_flag u(1) ... }
[0257] For example, general_constraint_info( ) may be referred to
as a general constraint information field or information on
constraint flags.
[0258] The semantics of syntax elements included in the syntax of
Table 31 may include, for example, matters disclosed in the
following table.
TABLE-US-00032 TABLE 32 no_lmcs_constraint_flag equal to 1
specifies that sps_lmcs_enabled_flag shall be equal to 0.
no_lmcs_constraint_flag equal to 0 does not impose such a
constraint.
[0259] sps_lmcs_enabled_flag included in Table 32 may be
substantially the same as sps_reshaper_enabled_flag included in
Table 25 described above. According to the above-described
embodiment including a constraint flag (ex.
no_lmcs_constraint_flag), the usage of the reshaping model
(reshaping model, reshaper, LMCS model, LMCS data) or reshaping (or
mapping, LMCS) may be constrained. For example, the constraint flag
for reshaping (or mapping, LMCS) may be expressed in various syntax
elements such as lmcs_constraint_flag, lmcs_data_constraint_flag,
no_lmcs_data_constraint_flag, no_lmcs_constraint_flag, etc. in the
general constraint information syntax (ex. general_constraint_info(
)).
[0260] The following drawings are created to explain specific
examples of the present specification. Since the names of specific
apparatus described in the drawings or the names of specific
signals/messages/fields are presented by way of example, the
technical features of the present specification are not limited to
the specific names used in the following drawings.
[0261] FIG. 13 and FIG. 14 schematically show an example of a
video/image encoding method and related components according to
embodiment(s) of the present document. The method disclosed in FIG.
13 may be performed by the encoding apparatus disclosed in FIG. 2.
Specifically, for example, S1300 of FIG. 13 may be performed by the
adder 250 of the encoding apparatus, and S1310 may be performed by
the residual processor 230 of the encoding apparatus, and S1320 may
be performed by the entropy encoder 240 of the encoding apparatus.
The method disclosed in FIG. 13 may include the embodiments
described above in the present document.
[0262] Referring to FIG. 13, the encoding apparatus may generate
reconstructed luma samples of the current block in the current
picture (S1300). In one example, the encoding apparatus may perform
the prediction for the original luma samples (luma component of the
original samples). The encoding apparatus may derive the prediction
mode of the current block as the intra prediction mode or the inter
prediction mode, and may generate prediction luma samples by
performing the prediction for the original luma samples (luma
component of the original samples) based on the prediction mode of
the current block. In this case, various prediction methods
disclosed in the present document, such as inter prediction or
intra prediction, may be applied. The encoding apparatus may
generate reconstructed luma samples based on the prediction luma
samples and/or the original luma samples.
[0263] As one example, the encoding apparatus may derive reshaping
codewords for a reshaping process of luma prediction samples. For
example, the reshaping codewords may be RspCW[i] described in
conjunction with Equation 7 and/or Table 19. Also, the encoding
apparatus may derive information on reshaping codewords for the
reshaping process of reconstructed luma samples. For example,
information about reshaping codewords may include
reshaper_model_bin_delta_abs_cw_prec_minus1,
reshape_model_bin_delta_abs_CW[i],
reshaper_model_bin_delta_sign_CW_flag[i], and/or RspDeltaCW[i]
described in conjunction with Equation 6, Table 17 and/or Table
18.
[0264] As one example, the encoding apparatus may further derive
reshaper model indices for reshaping process. The reshaper model
indices may include at least one of syntax elements included in
reshaper model information (syntax) and header information (tile
group header, picture header, or slice header). For example, the
reshaper model indices may include the above-described
reshaper_model_min_bin_idx, reshaper_model_delta_max_bin_idx,
reshape_model_max_bin_idx, and MaxBinIdx. For example, the reshaper
model indices may be included in the reshaper model in a parameter
set (i.e., an adaptation parameter set).
[0265] For example, the encoding apparatus may generate modified
reconstructed luma samples based on the reconstructed luma samples
and the reshaping codewords. The modified reconstructed luma
samples may be generated based on forward reshaping or inverse
reshaping. The modified reconstructed luma samples may be referred
to as (forward or inverse) mapped luma prediction samples.
[0266] The encoding apparatus may generate reshaping related
information (S1310). The reshaping related information may include
information on reshaping codewords, information on reshaper model
indices and information on the reshaper model (reshaping data
field) described above in the present document. For example, the
reshaping related information may further include information on
modified reconstructed luma samples.
[0267] The encoding apparatus may encode video/image information
(S1320). The image/video information may include information for
generating the reconstructed luma samples and information related
to the reshaping. The information for generating the reconstructed
luma samples may include, for example, prediction related
information (prediction mode information), residual information,
LMCS related information (information on reshaping (reshaper,
reshaper data field, reshaper model)), and/or ALF related
information. The prediction related information may include
information on various prediction modes (i.e., merge mode, MVP
mode, etc.), MVD information, and the like.
[0268] The encoded image/video information may be output in the
form of a bitstream. The bitstream may be transmitted to the
decoding apparatus through a network or a storage medium.
[0269] The image/video information may include various information
according to an embodiment of the present document. For example,
the image/video information may include at least one information or
at least one syntax element disclosed in at least one of Tables 1,
3, 4, 7, 9, 13, 15, 17, 19, 20, 21, 23, 25, 27 and/or 29 described
above.
[0270] For example, the image information may include a first
adaptive parameter set (APS). The first APS may be implemented as
shown in Table 23 described above. The first APS may include type
information specifying that the first APS is an APS including a
reshaper model. For example, the type information may be
aps_params_type described together with Tables 23 and 24. Based on
the type information, the first APS may include a reshaper model.
That is, the first APS may be classified into an in-loop mapping
type (reshaper type or LMCS type) based on the reshaper related APS
ID information. The encoding apparatus may parse/signal the
reshaper model based on type information specifying that the first
APS is an APS including the reshaper model. Reshaping codewords,
information about them, and/or reshaping model indices may be
derived based on the reshaping model.
[0271] In one example (related to Table 24), based on the value of
the type information, specifying that the first APS is an APS
including the reshaper data field, is 1, the first APS may include
the reshaper model including reshaper model indices. Here, the
reshaper model indices may include at least one of syntax elements
included in reshaper model information (syntax) and header
information (tile group header, picture header, or slice header).
For example, the reshaper model indices may include the
above-described reshaper_model_min_bin_idx,
reshaper_model_delta_max_bin_idx, reshape_model_max_bin_idx, and
MaxBinIdx.
[0272] The image information may include a first header information
(for example, tile group header information or picture header
information), the first header information may include reshaper
related APS ID information, and the reshaper related APS ID
information may indicate an ID of the first APS.
[0273] In one example, the image information may include an SPS,
and the SPS may include a first reshaper enable flag (i.e.,
sps_reshaper_enabled_flag of Table 25) specifying whether the
reshaper model is enabled. When the value of the first reshaper
enabled flag is 1, the first header information may include a
second reshaper enabled flag (ex. tile_group_reshaper_enabled_flag
of Table 25 or ph_reshaper_enabled_flag) specifying whether the
reshaper model is enabled in a picture (in another example, a tile
group or a slice). When the value of the second reshaper enabled
flag is 1, the reshaper related APS ID information may be included
in the first header information.
[0274] The encoding apparatus may perform chroma residual scaling
based on the modified reconstructed luma samples and a chroma
residual scaling flag. The chroma residual scaling flag may be
included in the first header information, and the chroma residual
scaling flag may be generated when the value of the first reshaper
enabled flag is 1.
[0275] In one example, the encoding apparatus may generate
reconstructed samples based on the modified reconstructed luma
samples. The encoding apparatus may derive filter coefficients for
the ALF process on the reconstructed samples. The encoding
apparatus may generate modified reconstructed samples based on the
reconstructed samples and the filter coefficients. The encoding
apparatus may generate ALF data based on the filter coefficients
and/or the modified reconstructed samples.
[0276] For example, the image information may further include a
second APS. The second APS may be implemented as shown in Table 23
described above. The second APS may include type information
specifying that the second APS is an APS including an ALF data
field. For example, the type information may be aps_params_type
described together with Tables 23 and 24. Based on the type
information, the second APS may include an ALF data field. That is,
the second APS may be classified into an ALF type based on ALF
related APS ID information. The encoding apparatus may parse/signal
the ALF data field based on type information specifying that the
second APS is an APS including the ALF data field.
[0277] In one example, the image information may include second
header information (i.e., tile group header information or slice
header information). The second header information may include ALF
related APS ID information, and the ALF related APS ID information
may represent an ID of the second APS including the ALF data.
[0278] In one example, the ID of the first APS indicated by the
reshaper related APS ID information may be different from the ID of
the second APS indicated by the ALF related APS ID information.
[0279] For example (related to Tables 23 and 24), when the value of
the type information, specifying that the second APS is an APS
including the ALF data field, is 0, the APS parameters of the
second APS indicate the ALF parameters and the second APS may
include an ALF data field and/or ALF data. The filter coefficients
may be derived based on the ALF data field and/or ALF data.
[0280] In one example, the SPS may include a first ALF enabled flag
(i.e., sps_ALF_enabled_flag of Table 25) specifying whether the ALF
data is enabled. When the value of the first ALF enabled flag is 1,
the second header information includes a second ALF enabled flag
(ex. tile_group_alf_enabled_flag of Table 25 or
ph_alf_enabled_flag) specifying whether the ALF data is enabled in
a picture (in another example, a tile group or a slice). When the
value of the second ALF enabled flag is 1, the ALF related APS ID
information may be included in the second header information.
[0281] In one example, the image information may include a general
constraint information field (or information on constraint flags,
ex. general_constraint_infoo of Table 29). Furthermore, the general
constraint information field may include a constraint flag related
to the presence of the reshaper model. For example, the constraint
flag related to the presence of the reshaper model may be a
reshaper_model_present_constraint_flag included in Table 29 or
30.
[0282] In one example, the first header information may include an
indication flag specifying whether the reshaper model is present in
a first header (i.e., a tile group header or a picture header). For
example, the indication flag may be
tile_group_reshaper_model_present_flag included in Table 15 or 16.
When the value of the constraint flag is 1, the value of the
indication flag may be set to 1. Therefore, the reshaper model can
always be parsed according to the constraint flag (i.e., for an
intra random access point picture (IRAP picture), or for an intra
mode). When the value of the constraint flag is 0, the contraint
may not be applied (reshaper_model_present_constraint_flag equal to
0 does not impose a constraint).
[0283] In one example, the encoding apparatus may derive residual
samples based on the modified reconstructed luma samples and the
original samples. In this case, residual information may be derived
based on the residual samples. Based on the residual information,
(modified) residual samples may be derived. Reconstructed samples
may be generated based on the (modified) residual samples. A
reconstructed block and a reconstructed picture may be derived
based on the reconstructed samples.
[0284] FIG. 15 and FIG. 16 schematically show an example of an
image/video decoding method and related components according to an
embodiment of the present document. The method disclosed in FIG. 15
may be performed by the decoding apparatus illustrated in FIG. 3.
Specifically, for example, S1500 of FIG. 15 may be performed by the
entropy decoder 310 of the decoding apparatus, S1510 may be
performed by the adder 340 of the decoding apparatus, and S1520 may
be performed by the residual processor 320 of the decoding
apparatus. The method disclosed in FIG. 15 may include the
embodiments described above in the present document.
[0285] Referring to FIG. 15, the decoding apparatus may
receive/obtain image/video information (S1500). The decoding
apparatus may receive/obtain the image/video information from a
bitstream. For example, the decoding apparatus may obtain
prediction mode information and/or information on reshaping from
the bitstream.
[0286] The image/video information may include various information
according to an embodiment of the present document. For example,
the image/video information may include information disclosed in at
least one of Tables 1, 3, 4, 7, 9, 13, 15, 17, 19, 20, 21, 23, 25,
27, and/or 29 described above.
[0287] The decoding apparatus may generate reconstructed luma
samples of the current block in the current picture based on the
prediction mode information (S1510). In one example, the decoding
apparatus may perform prediction on original luma samples (a luma
component of the original samples). Prediction luma samples may be
generated by deriving the prediction mode of the current block in
the intra prediction mode or the inter prediction mode and
performing prediction on the original luma samples (luma component
of the original samples) based on the prediction mode of the
current block. In this case, various prediction methods disclosed
in the present document, such as inter prediction or intra
prediction, may be applied. The decoding apparatus may generate
reconstructed luma samples based on the predicted luma samples
and/or the original luma samples.
[0288] The decoding apparatus may perform a reshaping process on
the reconstructed luma samples (S1520). Specifically, the decoding
apparatus may derive reshaping codewords for the reshaping. Also,
the decoding apparatus may generate modified reconstructed luma
samples based on the reconstructed luma samples and the reshaping
codewords. In one example, the modified reconstructed luma samples
may be generated based on forward reshaping or inverse reshaping.
The modified reconstructed luma samples may be referred to as
(forward or inverse) mapped reconstructed luma samples or reshaped
reconstructed luma samples. Specifically, the decoding apparatus
may derive reshaping codewords based on the reshaping related
information. For example, information on reshaping codewords may
include reshaper_model_bin_delta_abs_cw_prec_minus1,
reshape_model_bin_delta_abs_CW [i],
reshaper_model_bin_delta_sign_CW_flag[i], and/or RspDeltaCW[i]
described in conjunction with Equation 6, Table 17 and/or Table
18.
[0289] In addition, the decoding apparatus may further derive
reshaping model indices for the reshaping process. The reshaper
model indices may include at least one of syntax elements included
in reshaper model information (syntax) and header information (tile
group header, picture header, or slice header). For example, the
reshaper model indices may include the above-described
reshaper_model_min_bin_idx, reshaper_model_delta_max_bin_idx,
reshape_model_max_bin_idx, and MaxBinIdx. The decoding apparatus
may perform a reshaping process on the reconstructed luma samples
based on the reshaping codewords and/or the reshaping model
indices.
[0290] For example, the image information may include a first
adaptive parameter set (APS). The first APS may be implemented as
shown in Table 23 described above. The first APS may include type
information specifying that the first APS is an APS including a
reshaper model. For example, the type information may be
aps_params_type described together with Tables 23 and 24. Based on
the type information, the first APS may include a reshaper model.
That is, the first APS may be classified into an in-loop mapping
type (reshaper type or LMCS type) based on the reshaper related APS
ID information. The decoding apparatus may parse/signal the
reshaper model based on type information specifying that the first
APS is an APS including the reshaper model. Reshaping codewords,
information about them, and/or reshaping model indices may be
derived based on the reshaping model.
[0291] In one example (related to Table 24), based on the value of
the type information, specifying that the first APS is an APS
including the reshaper data field, is 1, the first APS may include
the reshaper model including reshaper model indices. Here, the
reshaper model indices may include at least one of syntax elements
included in reshaper model information (syntax) and header
information (tile group header, picture header, or slice header).
For example, the reshaper model indices may include the
above-described reshaper_model_min_bin_idx,
reshaper_model_delta_max_bin_idx, reshape_model_max_bin_idx, and
MaxBinIdx.
[0292] The image information may include a first header information
(for example, tile group header information or picture header
information), the first header information may include reshaper
related APS ID information, and the reshaper related APS ID
information may indicate an ID of the first APS.
[0293] In one example, the image information may include an SPS,
and the SPS may include a first reshaper enable flag (i.e.,
sps_reshaper_enabled_flag of Table 25) specifying whether the
reshaper model is enabled. When the value of the first reshaper
enabled flag is 1, the first header information may include a
second reshaper enabled flag (ex. tile_group_reshaper_enabled_flag
of Table 25 or ph_reshaper_enabled_flag) specifying whether the
reshaper model is enabled in a picture (in another example, a tile
group or a slice). When the value of the second reshaper enabled
flag is 1, the reshaper related APS ID information may be included
in the first header information.
[0294] The decoding apparatus may perform chroma residual scaling
based on the modified reconstructed luma samples and a chroma
residual scaling flag. The chroma residual scaling flag may be
included in the first header information, and the chroma residual
scaling flag may be signaled when the value of the first reshaper
enabled flag is 1.
[0295] The decoding apparatus may generate reconstructed samples
based on the modified reconstructed luma samples. The decoding
apparatus may perform an ALF process on the reconstructed samples.
The decoding apparatus may derive filter coefficients for the ALF,
and generate modified reconstructed samples based on the
reconstructed samples and the filter coefficients. One filter may
include a set of filter coefficients. The filter or the filter
coefficients may be derived based on the ALF data.
[0296] For example, the image information may further include a
second APS. The second APS may be implemented as shown in Table 23
described above. The second APS may include type information
specifying that the second APS is an APS including an ALF data
field. For example, the type information may be aps_params_type
described together with Tables 23 and 24. Based on the type
information, the second APS may include an ALF data field. That is,
the second APS may be classified into an ALF type based on ALF
related APS ID information. The decoding apparatus may parse/signal
the ALF data field based on type information specifying that the
second APS is an APS including the ALF data field.
[0297] In one example, the image information may include second
header information (i.e., tile group header information or slice
header information). The second header information may include ALF
related APS ID information, and the ALF related APS ID information
may represent an ID of the second APS including the ALF data.
[0298] In one example, the ID of the first APS indicated by the
reshaper related APS ID information may be different from the ID of
the second APS indicated by the ALF related APS ID information.
[0299] For example (related to Tables 23 and 24), when the value of
the type information, specifying that the second APS is an APS
including the ALF data field, is 0, the APS parameters of the
second APS indicate the ALF parameters and the second APS may
include an ALF data field and/or ALF data. The filter coefficients
may be derived based on the ALF data field and/or ALF data.
[0300] In one example, the SPS may include a first ALF enabled flag
(i.e., sps_ALF_enabled_flag of Table 25) specifying whether the ALF
data is enabled. When the value of the first ALF enabled flag is 1,
the second header information includes a second ALF enabled flag
(ex. tile_group_alf_enabled_flag of Table 25 or
ph_alf_enabled_flag) specifying whether the ALF data is enabled in
a picture (in another example, a tile group or a slice). When the
value of the second ALF enabled flag is 1, the ALF related APS ID
information may be included in the second header information.
[0301] In one example, the image information may include a general
constraint information field (or information on constraint flags,
ex. general_constraint_infoo of Table 29). Furthermore, the general
constraint information field may include a constraint flag related
to the presence of the reshaper model. For example, the constraint
flag related to the presence of the reshaper model may be a
reshaper_model_present_constraint_flag included in Table 29 or
30.
[0302] In one example, the first header information may include an
indication flag specifying whether the reshaper model is present in
a first header (i.e., a tile group header or a picture header). For
example, the indication flag may be
tile_group_reshaper_model_present_flag included in Table 15 or 16.
When the value of the constraint flag is 1, the value of the
indication flag may be set to 1. Therefore, the reshaper model can
always be parsed according to the constraint flag (i.e., for an
intra random access point picture (IRAP picture), or for an intra
mode). When the value of the constraint flag is 0, the contraint
may not be applied (reshaper_model_present_constraint_flag equal to
0 does not impose a constraint).
[0303] In the above-described embodiment, the methods are described
based on the flowchart having a series of steps or blocks. The
present disclosure is not limited to the order of the above steps
or blocks. Some steps or blocks may occur simultaneously or in a
different order from other steps or blocks as described above.
Further, those skilled in the art will understand that the steps
shown in the above flowchart are not exclusive, that further steps
may be included, or that one or more steps in the flowchart may be
deleted without affecting the scope of the present disclosure.
[0304] The method according to the above-described embodiments of
the present document may be implemented in software form, and the
encoding apparatus and/or decoding apparatus according to the
present document is, for example, may be included in the apparatus
that performs the image processing of a TV, a computer, a smart
phone, a set-top box, a display device, etc.
[0305] When the embodiments in the present document are implemented
in software, the above-described method may be implemented as a
module (process, function, etc.) that performs the above-described
function. A module may be stored in a memory and executed by a
processor. The memory may be internal or external to the processor,
and may be coupled to the processor by various well-known means.
The processor may include an application-specific integrated
circuit (ASIC), other chipsets, logic circuits, and/or data
processing devices. Memory may include read-only memory (ROM),
random access memory (RAM), flash memory, memory cards, storage
media, and/or other storage devices. That is, the embodiments
described in the present document may be implemented and performed
on a processor, a microprocessor, a controller, or a chip. For
example, the functional units shown in each figure may be
implemented and performed on a computer, a processor, a
microprocessor, a controller, or a chip. In this case, information
on instructions or an algorithm for implementation may be stored in
a digital storage medium.
[0306] In addition, the decoding apparatus and the encoding
apparatus to which the present disclosure is applied may be
included in a multimedia broadcasting transmission/reception
apparatus, a mobile communication terminal, a home cinema video
apparatus, a digital cinema video apparatus, a surveillance camera,
a video chatting apparatus, a real-time communication apparatus
such as video communication, a mobile streaming apparatus, a
storage medium, a camcorder, a VoD service providing apparatus, an
Over the top (OTT) video apparatus, an Internet streaming service
providing apparatus, a three-dimensional (3D) video apparatus, a
teleconference video apparatus, a transportation user equipment
(i.e., vehicle user equipment, an airplane user equipment, a ship
user equipment, etc.) and a medical video apparatus and may be used
to process video signals and data signals. For example, the Over
the top (OTT) video apparatus may include a game console, a
blue-ray player, an internet access TV, a home theater system, a
smart phone, a tablet PC, a Digital Video Recorder (DVR), and the
like.
[0307] Furthermore, the processing method to which the present
document is applied may be produced in the form of a program that
is to be executed by a computer and may be stored in a
computer-readable recording medium. Multimedia data having a data
structure according to the present disclosure may also be stored in
computer-readable recording media. The computer-readable recording
media include all types of storage devices in which data readable
by a computer system is stored. The computer-readable recording
media may include a BD, a Universal Serial Bus (USB), ROM, PROM,
EPROM, EEPROM, RAM, CD-ROM, a magnetic tape, a floppy disk, and an
optical data storage device, for example. Furthermore, the
computer-readable recording media includes media implemented in the
form of carrier waves (i.e., transmission through the Internet). In
addition, a bitstream generated by the encoding method may be
stored in a computer-readable recording medium or may be
transmitted over wired/wireless communication networks.
[0308] In addition, the embodiments of the present document may be
implemented with a computer program product according to program
codes, and the program codes may be performed in a computer by the
embodiments of the present document. The program codes may be
stored on a carrier which is readable by a computer.
[0309] FIG. 17 shows an example of a content streaming system to
which embodiments disclosed in the present document may be
applied.
[0310] Referring to FIG. 17, the content streaming system to which
the embodiment(s) of the present document is applied may largely
include an encoding server, a streaming server, a web server, a
media storage, a user device, and a multimedia input device.
[0311] The encoding server compresses content input from multimedia
input devices such as a smartphone, a camera, a camcorder, etc.
Into digital data to generate a bitstream and transmit the
bitstream to the streaming server. As another example, when the
multimedia input devices such as smartphones, cameras, camcorders,
etc. directly generate a bitstream, the encoding server may be
omitted.
[0312] The bitstream may be generated by an encoding method or a
bitstream generating method to which the embodiment(s) of the
present disclosure is applied, and the streaming server may
temporarily store the bitstream in the process of transmitting or
receiving the bitstream.
[0313] The streaming server transmits the multimedia data to the
user device based on a user's request through the web server, and
the web server serves as a medium for informing the user of a
service. When the user requests a desired service from the web
server, the web server delivers it to a streaming server, and the
streaming server transmits multimedia data to the user. In this
case, the content streaming system may include a separate control
server. In this case, the control server serves to control a
command/response between devices in the content streaming
system.
[0314] The streaming server may receive content from a media
storage and/or an encoding server. For example, when the content is
received from the encoding server, the content may be received in
real time. In this case, in order to provide a smooth streaming
service, the streaming server may store the bitstream for a
predetermined time.
[0315] Examples of the user device may include a mobile phone, a
smartphone, a laptop computer, a digital broadcasting terminal, a
personal digital assistant (PDA), a portable multimedia player
(PMP), navigation, a slate PC, tablet PCs, ultrabooks, wearable
devices (ex. Smartwatches, smart glasses, head mounted displays),
digital TVs, desktops computer, digital signage, and the like. Each
server in the content streaming system may be operated as a
distributed server, in which case data received from each server
may be distributed.
[0316] Each server in the content streaming system may be operated
as a distributed server, and in this case, data received from each
server may be distributed and processed.
[0317] The claims described herein may be combined in various ways.
For example, the technical features of the method claims of the
present document may be combined and implemented as an apparatus,
and the technical features of the apparatus claims of the present
document may be combined and implemented as a method. In addition,
the technical features of the method claim of the present document
and the technical features of the apparatus claim may be combined
to be implemented as an apparatus, and the technical features of
the method claim of the present document and the technical features
of the apparatus claim may be combined and implemented as a
method.
* * * * *